Interesting; the join protocol is pretty complicated.
As an aside, re-reading the note you posted I've since convinced myself that the reason I couldn't get that GE plug to pair on channel 18 is that it was using only the 'preferred channel mask' (per the Zigbee HA 1.2 spec) channels 11,14,15,19,20,24 and 25 on its initial scan during a join after reset; once joined its perfectly capable of doing a channel change 'on the fly' by scanning all standard Zigbee channels (just my luck I picked 18 when I set up my C-3). I suspect that's why that GE branded model (45852, purchased in 2019) was quickly replaced by another that appears otherwise identical.
The channel change process is actually quick and usually goes off without a hitch. in moving that old plug around testing C-3, C-7, and C-8 I swapped channels on my Zigbee network about 6 times yesterday. Even on the C-3 with 70+ devices, they all followed channel changes flawlessly within a minute or so (only two failed to properly change during one of the swaps, both just required a battery pull/reinsert, no reset required).