I'd count the last three, but not the CGII or RX. The TG-16 and PAL TurboGrafx are also unique enough to count as variations and not simply revisions.
There's also the Vistar, Sharp X-1 Twin.
Here's what I'd list all together-
PC Engine
CoreGrafx
PC Engine Shuttle
PC Engine LT
PC Engine Duo
PC Engine Duo-R
Pioneer LaserActive
PC Engine GT
SuperGrafx
Vistar
Sharp X-1 Twin
If counting silly revisions within models, like the HDG and non-HDG Model 1 Genesis', then we'll never be able to compare consoles since there are likely hundreds of different revisions across models of each console and most aren't widely documented.