Hey guys, I'm still here!
The resistor thing is correct... I think earlier versions had separate firmware forks, which may have required the hardware AND firmware change, but at some point they merged (I think I noticed this as of 2.130?) so you can "upgrade" any board by just adding the right resistors. *Note that the earliest ET boards had a smaller chip that won't take the current firmware.
Similar tricks exist to make a "Lite" indoor or wireless controller into a regular one, I haven't posted anything about it here for fear of legal reprisal against TFP, but pm me if you're interested.
Hardware manufacturers have been doing this sort of thing for ages - it's super cost effective although it can be construed as somewhat deceitful? maybe? I dunno... it IS their proprietary information afterall, so it's probably appropriate to not shout it from the rooftops considering the state of the right to repair laws these days
