[Droid Turbo 2 General] implausibleg:
Preflash validation failed

I'm am new to this stuff and trying my darndest to fix my mother's water damaged Verizon DT2 which gets stuck in a bootloop until the device is powered off from the fastboot menu (which I can reach without issue). On two different Windows machines I can not get RSD Lite to display the phone, even though the device is listed under the Device Manager and the serial number comes up with 'fastboot devices' (although not coming up with 'adb devices' - assuming because USB debugging was not enabled??). Because the bootloader is unlockable as far as I have read online for this device, usb debugging was not enabled before the soft-brick event, and I can't get the device to show up in RSD Lite, in my VERY limited experience in these matters it appears my only option is using fastboot (most of my attempts are with mfastboot-v2). The problem is every firmware I have downloaded and tried, in both 5.1.1 and 6.0 varieties (for what I believe is my region - US) is giving me a 'Preflash validation failed' error when attempting to flash boot, recovery, partition and system. Other aspects appear to write and flash just fine. I'm assuming this has to do with the phone not recognizing these items as stock firmware, but I have no clue how this works.

Example of a batch file and output for an attempt (each attempt with various firmware downloads gives similar results) ...

Batch-

echo off
mfastboot getvar max-sparse-size
mfastboot oem fb_mode_set
mfastboot flash partition gpt.bin
mfastboot flash bootloader bootloader.img
mfastboot flash logo logo.bin
mfastboot flash boot boot.img
mfastboot flash -S 512M recovery recovery.img
mfastboot flash -S 512M system system.img_sparsechunk.0
mfastboot flash -S 512M system system.img_sparsechunk.1
mfastboot flash -S 512M system system.img_sparsechunk.2
mfastboot flash -S 512M system system.img_sparsechunk.3
mfastboot flash -S 512M system system.img_sparsechunk.4
mfastboot flash -S 512M system system.img_sparsechunk.5
mfastboot flash -S 512M system system.img_sparsechunk.6
mfastboot flash -S 512M system system.img_sparsechunk.7
mfastboot flash -S 512M system system.img_sparsechunk.8
mfastboot flash -S 512M system system.img_sparsechunk.9
mfastboot flash -S 512M system system.img_sparsechunk.10
mfastboot flash -S 512M system system.img_sparsechunk.11
mfastboot flash -S 512M system system.img_sparsechunk.12
mfastboot flash -S 512M system system.img_sparsechunk.13
mfastboot flash -S 512M system system.img_sparsechunk.14
mfastboot flash modem NON-HLOS.bin
mfastboot flash bluetooth BTFM.bin
mfastboot flash fsg fsg.mbn
mfastboot erase modemst1
mfastboot erase modemst2
mfastboot erase cache
mfastboot erase userdata
mfastboot erase customize
mfastboot erase clogo
mfastboot flash fsg fsg.mbn
mfastboot flash bluetooth BTFM.bin
mfastboot oem fb_mode_clear
echo -------------------------------------------------------------------------
echo please scroll up and check your flash for any errors
echo -------------------------------------------------------------------------
pause
mfastboot reboot
exit

Result-

echo of
f
max-sparse-size: 268435456
finished. total time: 0.000s
...
OKAY [ -0.000s]
finished. total time: -0.000s
target max-sparse-size: 256MB
sending 'partition' (32 KB)...
OKAY [ 0.000s]
writing 'partition'...
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 0.328s
target max-sparse-size: 256MB
sending 'bootloader' (2781 KB)...
OKAY [ 0.063s]
writing 'bootloader'...
(bootloader) flashing aboot ...
(bootloader) flashing sbl1 ...
(bootloader) flashing pmic ...
(bootloader) flashing rpm ...
(bootloader) flashing tz ...
(bootloader) flashing hyp ...
(bootloader) flashing sdi ...
OKAY [ 1.496s]
finished. total time: 1.574s
target max-sparse-size: 256MB
sending 'logo' (2602 KB)...
OKAY [ 0.063s]
writing 'logo'...
OKAY [ 0.063s]
finished. total time: 0.125s
target max-sparse-size: 256MB
sending 'boot' (40960 KB)...
OKAY [ 0.927s]
writing 'boot'...
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 1.599s
sending 'recovery' (41040 KB)...
OKAY [ 0.935s]
writing 'recovery'...
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 1.589s
sending 'system' (256893 KB)...
OKAY [ 5.516s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 5.892s
sending 'system' (255974 KB)...
OKAY [ 5.513s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 5.529s
sending 'system' (259709 KB)...
OKAY [ 5.573s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 5.589s
sending 'system' (252798 KB)...
OKAY [ 5.425s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 5.456s
sending 'system' (255535 KB)...
OKAY [ 5.503s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 5.550s
sending 'system' (257581 KB)...
OKAY [ 5.538s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 5.554s
sending 'system' (255058 KB)...
OKAY [ 5.506s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 5.553s
sending 'system' (256897 KB)...
OKAY [ 5.508s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 5.534s
sending 'system' (255207 KB)...
OKAY [ 5.499s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 5.546s
sending 'system' (258044 KB)...
OKAY [ 5.535s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 5.551s
sending 'system' (257011 KB)...
OKAY [ 5.529s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 5.561s
sending 'system' (256325 KB)...
OKAY [ 5.513s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 5.528s
sending 'system' (253342 KB)...
OKAY [ 5.437s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 5.468s
sending 'system' (256765 KB)...
OKAY [ 5.524s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 5.540s
sending 'system' (130376 KB)...
OKAY [ 2.803s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 2.819s
target max-sparse-size: 256MB
sending 'modem' (40476 KB)...
OKAY [ 0.876s]
writing 'modem'...
OKAY [ 0.969s]
finished. total time: 1.861s
target max-sparse-size: 256MB
sending 'bluetooth' (1296 KB)...
OKAY [ 0.031s]
writing 'bluetooth'...
OKAY [ 0.049s]
finished. total time: 0.096s
target max-sparse-size: 256MB
sending 'fsg' (1480 KB)...
OKAY [ 0.031s]
writing 'fsg'...
OKAY [ 0.063s]
finished. total time: 0.094s
erasing 'modemst1'...
OKAY [ -0.000s]
finished. total time: -0.000s
erasing 'modemst2'...
OKAY [ -0.000s]
finished. total time: -0.000s
erasing 'cache'...
OKAY [ 0.016s]
finished. total time: 0.016s
erasing 'userdata'...
OKAY [ 0.359s]
finished. total time: 0.359s
erasing 'customize'...
OKAY [ 0.000s]
finished. total time: 0.000s
erasing 'clogo'...
OKAY [ -0.000s]
finished. total time: -0.000s
target max-sparse-size: 256MB
sending 'fsg' (1480 KB)...
OKAY [ 0.047s]
writing 'fsg'...
OKAY [ 0.047s]
finished. total time: 0.094s
target max-sparse-size: 256MB
sending 'bluetooth' (1296 KB)...
OKAY [ 0.031s]
writing 'bluetooth'...
OKAY [ 0.032s]
finished. total time: 0.094s
...
OKAY [ -0.000s]
finished. total time: -0.000s
-------------------------------------------------------------------------
please scroll up and check your flash for any errors
-------------------------------------------------------------------------
Press any key to continue . . .

Any guidance is greatly appreciated - more than you know!!!!!

EDIT: More info on the batch script - The core of the batch file was generated from the xml using rootjunkysdl.com's tool and then I changed fastboot to mfastboot on most attempts and added the '-S 512M' as the results without seemed to be complaining about the sparse sizes without this. I think I have tried most of the firmwares without the sparse size limit.