I ran into many issues trying to get the OTA update to work properly with upgrading the bootloader and radio.
Long story short, I had to do it manually and only after the full system images were released.
If you are running into the problem where the bootloader isn't updated or your radio baseband is showing one thing in bootloader and another in the system status, here is a quick fix:
1) Download the full system image from Google. Untar and unzip.
2) Fastboot flash the bootloader (4.18). Fastboot reboot bootloader. Verify that the version is correct and updated.
3) Fastboot flash the STOCK 4.2.2 RECOVERY. Do not attempt to use CWM or TWRP, otherwise you will have issues.
4) Fastboot flash the 1231_0.17... radio.
5) Reboot into (stock) recovery mode.
6) At this point, the stock recovery should begin to process the radio update and do the actual installation of it. You will see the progress bar moving. When it's done, the tab will automatically reboot into normal mode.
7) Verify that your radio (in system settings) is updated to the latest version.
8) Reflash custom recovery if you want.
After many wasted hours dealing with this issue when the update first came out (OTA), it seems to be related to the bach_update.modem function not being present in custom recoveries. Unlike the system, boot, etc. image files, the radio update is not an actual "image", at least like the others. While it is an ext4 filesystem system, the way it works is more similar to a recovery flashable zip file. It has a set of instructions for recovery to install the radio update. Custom recoveries break at this point, and so far I've only been able to get the stock one to work properly. For some reason, failing on the radio can also break the bootloader update as well, not to mention the build.prop update which is after the radio and might result in an incorrect Android version being identified.