Well I finally got home and downloaded the update.... looked inside the firmware-update folder inside the zip file, and looked at the files within the firmware-update folder.... same files as 8.9.20, and 8.9.13.... since there was no anti-update within the previous 2 updates, I'm going to go out on a limb here and say that there are no anti-update files in this folder either...
BTFM.bin - Bluetooth driver
dspso.bin - digital signal processing driver
NON-HLOS.bin - modem driver
cmnlib.mbn + cmnlib64.mbn - common library files (probably need updating to support the driver updates)
devcgf.mbn - device configuration file (probably to tell the device how to find/recognize the new drivers)
Keymaster.mbn - something to do with encryption, or low-level access... (Google it and read for hours)
splash.img - your bootloader splash screen image.
I was able to figure out these files from GOOGLE
Theres nothing in here that updates your bootloader... ingbrzy removes those files...