I think the only reason I never had a problem going from Poser 5 to DS2, DS 3A, DS 4.0P, and then back to Poser 9 was, I rarely bought anything that was DS only. All my older products I purchased at various stores were all Poser compatible, so the Runtime folders were the same in both. The only difference back then was, DS2 and DS3 versions didn't have access to the Materials Library, so folks were creating .PZ2 files to apply textures, though I always placed the .MC6 and .MT5 files in the Materials Library anyway. That changed with DS 4.0, and now I can use everything in my DS 3A Runtime in Poser without problems. My DS 4.0 content is all Genesis 1 related, so I can't use that in Poser, but that's a small Runtime compared to DS 3A.