Old saves "should" still work. However, there are new scenes and images that will be unavailable if you load ahead of them, as they were added to early parts of the game (most of these scenes concern Rachel).
There are also new variables to some events, so there's a chance even some new events might not fire for sure.
I heavily recommend starting a new game. We don't expect to ask you to restart again in the next few updates (hopefully never tbh), as we have finished proofreading almost all the old content and revamping some scenes that were causing trouble.