Will a 1989 Suzuki DT15C lower unit fit earlier 9.9s and 15s?

[Chinewalker]

I'm trying to see what motors my 1989 Suzuki DT15C lower unit will fit. Offhand, it looks like it'll only fit 1989-1997 DT15C models. But, in poking around with the parts listings it appears Suzuki changed things up starting in 1989, and the diagrams look pretty much the same pre and post 1989. Some of the part numbers stay the same while others change. 1989 & newer 9.9s and 15s used different lowers, but 1988 & earlier seem to use the same.

THE QUESTIONS...
Was it subtle differences preventing the '89 15 unit from fitting, say, an '86 9.9/15 or are they compatible? I don't deal much with the Suzukis, so this is pretty new to me... I know with the Johnrudes and Mercs there can be some differences in part number as they improve or modify a part, but the later version is still compatible with the earlier version.

Thanks!