[Nook HD, HD+ Android Development] Diagon:
Thanks nmyshkin. I got a bit frustrated by the date issue and finding the ROM's, so I went through all those folders and listed what we have for the acclaim (below). For a couple the "creation date" and the "modified date" are different, which explains some of the confusion.

I've been trying to install the newest LNOS, but was having the same trouble you were with root. Then I discovered amaces' Selected FAQ. In point 2 he describes that for LNOS, we have two ways of getting root. We can use the offical addon-on, and then turn on root by this method. Or, we can "install phh's SU and manager, like on AOSP." So it dawned on me that I should flash addonsu-phh-arm.zip (which I found in obsolete) and then on reboot, install phh's superuser manager from f-drod. That worked!

Earlier, I had tried getting the LNOS offical addon (dated 2017.06.21) and turning it on by the method described in that link (tapping Build Number 7 times ...) I couldn't get it to work. It then dawned on me that maybe amaces' addonsu-14.1-arm.zip (2018.02.11/2018.12.01) and addonsu-14.1-arm-new.zip (2017.06.14, in ~/obsolete) are earlier versions of LNOS's official addon - perhaps even modified, I don't know. So I tried the former, now armed with the Build Number trick (which I hadn't known the first time I tried). That also worked! I was able to get root without PHH's superuser manager, via Settings >> Developer Tools! And, you'll be happy to know, Kodi is also running fine. :)

By the way, I found the "Root Verifier" utility in F-Droid to be useful.

[I will add that I still have not figured out how to install open_gapps-arm-7.1-pico-20201209.zip. TWRP complains about there not being enough room. I don't really need it, but I'd still like to know ...]

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addonsu* in ~:

Created Feb 11, 2018, modified Dec. 1, 2018: addonsu-14.1-arm.zip

addonsu* in ~/obsolete:

June 14, 2017: addonsu-14.1-arm-new.zip

June 14, 2017: addonsu-phh-arm.zip

lnos_acclaim* in ~/acclaim:

Jul 13, 2018: lnos_acclaim-ota-NJH47F.180713.zip (@Diagon: not working with non-obsolete addonsu)

lnos_acclaim* in ~/obsolete:

June 24, 2018: lnos_acclaim-ota-NJH47F.180624.zip

Feb 11, 2018: lnos_acclaim-ota-NJH47F.180211.zip (@nmyshkin: works with non-obsolete addonsu )

Oct 21, 2017: lnos_acclaim-ota-NJH47F.171021.zip

Many more from 2017:

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/194284828538

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/183387854409

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/167015800286

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/160119425778

aosp_acclaim* in ~/acclaim:

Jul 12, 2018: aosp_acclaim-ota-N2G48H.180713.zip

Aug 20, 2016: aosp_acclaim-ota-MOB30Z.160820.zip

aosp_acclaim* in ~/obsolete:

Feb 11, 2018: aosp_acclaim-ota-N2G48H.180212.zip

Dec 6, 2017: aosp_acclaim-ota-N2G48H.171206.zip

Many more from 2017:

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/239786866386

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/181740463774

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/174211215128

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/166931447258

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/160110315881

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/155563266439

Many more from 2016:

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/99602620259

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/73494456549

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/69855406537

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/65739412537

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/63777554973

https://notredame.app.box.com/s/26a4bygh9vbaw7jjq08xr5evomvaw5ww/file/63636884797