Theoretically, everything that wasn't touched in the update should be fine. That said, this could include anything in the new update and outside of it. If Tinkerer had to change a variable or flag that was part of the old content, the test save could behave weirdly or not work at all.Little question, is the save from the test version usable in the full release? I lost my HD and was thinking of getting to near where i was before i lost my saves before the full release.
I personally have kept test saves, but I'm usually up to date in terms of content and the only thing in those saves that changed was the new content. I experienced 1 bug, and that is that a quest to take the swamp elf on a date is marked incomplete (a flag change somewhere when the quest log was implemented), but the game still functions like I finished it.