Mixing and matching the sun/planetary combo into the wrong year combo definitely doesn’t work, tried that myself.
I looked closely at my annulus gears and couldn’t see a difference, and the 94-96 and 97-99 parts manuals both show the same part number for annulus gears. I actually compared 3 of them…1987 (old), 1994 (old), 1995 (new) and they all looked the same to me. I do know the 1987-1993 had a different part number, but o don’t know what the differences are. Maybe my 94 had the old part number, but the 94-96 catalog showed only one part number and it definitely differentiates between old and new part numbers for all the inputs, planetaries, etc. So I would think if there were two annulus part numbers in 94-96, they would have both been listed. Who knows.
I assumed the binding of gear teeth when installing planetary into the wrong case was some other dimensional issue, like maybe a difference in where the annulus is located in the case half or something. The gear itself seemed the same.
I am patiently waiting to watch and see how it goes once the gear is fully installed.