Is the Bootloader part of, or entity different to the Fastboot Loader?
At the moment my Shield TV is dead… Not even the nVIDIA Logo comes up at this point.
I can via the assist of a Netbook, get into the Fastboot Mode though. Where I can make a play at trying to flash what I can (Namely the 2015 Pro 3.3.0 Stock Recovery*), with reported success. I even tossed in a

$ fastboot -w

just for good measure. Alas for not.

So now I’m actually for once confused as to what may or may not be a Bootloader.

*Not to be confused with the actual recovery.img File which is a singular part of it.