The only thing I've noticed that can get a bit screwy if you start opening B5 files in B5.5 or the other way round is if you try and resume a render in one that you started in the other - DAZ did some "optimizing" of the render code in 5.5 that means its passes are different to those in B5 and so sometimes it gets a bit out of sync with where it should be.

 

Also, B5.5's resume render feature can be a bit unreliable on its own anyway (without going anywhere near B5).

Dreams are just nightmares on prozac...
Digital WasteLanD