[X Style (Pure) Q&A, Help & Troubleshooting] ResistanceIsFutile:
Not quite sure what's meant by your own meaning of Baseband. Your more than likely going to be answered by people still using the phone in different degrees of knowledge.

The experienced with a real practical application of this XT1575 device mostly have moved on to another device by now - but will any left on it be answering you. I'm glad to see [MENTION=2444885]aybarrap1[/MENTION] has answered.

[MENTION=5593145]stevejohnson42[/MENTION] uses the XT1575 too, and reports here and there of his flasholic tendencies on this device - might be helpful in any Nougat based ROM's to use the search box there and see if he's added anything in it.

Custom ROM Marshmallow development was always greater cause the XT1575 stayed on the Marshmallow OS for so long and because of Motorola not releasing Nougat sooner for it.

There are some Custom ROMS based on Nougat - just read their OP's to understand what's being required to using each one of them...

Nougat ROMs built for a Stock Nougat Kernel and Modem.

To answer your question without you going into a Blackhole in having to know more about your device in getting it back to good ground - I OFFER THIS-

Only way I know is to buy a XT1575 device that's never taken the servers Nougat OTA or has been ADB flashed to Nougat OS...

This as in ADB flashed questioned basically being understood by the device still having the bootloader status to LOCKED - as DEVICE LOCKED, the STATUS will still show 0, and it's software status of OFFICIAL.

Note:

The Status Code will always show 2 = (relocked) or 3 = (unlocked), and it can never go back to 0 = (device locked), if it's ever been unlocked by a Motorola token code obtained from their site.

Otherwise you need an image of the Bootloader screen of the device up for sale.

THAT'S THE ONLY WAYS TO KNOW AND A SELLER SHOULD SUPPLY THIS AS A GUARANTEE AND/OR AN IMAGE SHOWING YOU FIRST...

OR YOU BUYING FROM A SITE AND ASKING THESE QUESTION OF THE XT1575 SELLER FIRST BEFORE THE PURCHASE AND THE SITE (LIKE EBAY) HAS A GUARANTEE IN THAT AD - TO FALL BACK ON...

To check this yourself-

1. Using (vol down + power button) put the device in bootloader mode where all of this is visible / should read as follows - see images also.

(A) - totally Stock non-rooted Marshmallow Baseband should read as - M8992_1255331.29.01.88.02R SUPER_NA

as taken from my Marshmallow XT1575 build MPHS24.49-18-16 devices Bootloader.

(B) - Shows the very same thing with device from the ABOUT PHONE in settings.

(C) - Rooted Custom Rom Nougat Baseband M8992_1255331.29.01.88.09R - from the ABOUT PHONE in settings / using the NuclearROM.

(D) - M8992_1255331.29.01.88.09R SUPER_NA - from the Bootloader Mode on same device - using the NuclearROM.

PS: I'm thinking, changing to a different Android build changes the Baseband build as well being applicable to the OS build version.

Warning:::

No don't ever do a complete ADB MM downgrade flash - if wanting to OTA back up to Nougat at some future point after already being on the Nougat OS.

To be clear "It's not recommended to downgrade" and allow a Moto X Pure device in taking the Nougat OTA again.

Once bootloader.img and gpt.bin are updated, there is no reverting back without the serious and the likely risk of a hard-bricked device. Only remedy at this time is a mainboard replacement. Confirmed in this threads post #75 .

A COUPLE POINTS - I'd like to make:

I've always clean flashed my XT1575 in custom roms and to going back in a stock Nougat OS - point being, I have never had any problems thereafter...

Another thing I'm thinking with an LOS based ROM - writes / changes some partitions parts that only with your ADB flashing back to the factory Official Stock Nougat can fix - changing everything back to an original partition structure.

- TWRP only backups a few partitions on the device, so partitions out of it's reach never gets restored back to an original stock environment with a TWRP backup when you do a restore using it/one made thereafter.

OTHER Reading you might want to do:

#30

#61

#73

#147

#179

#184

Baseband

I'm far from being a real practical experienced user in a XT1575 device but, I share in what I've taken a grasp of.

Hope this helps :)