I went to 2012b to 2012c to 2012d with no problems. With that being said, I also added E1.31 this year and that caused some issues a long the way with mapping of lights.
So fslopex1950, you'd probably need to attach your xlights network config, or take a screenshot of it and attach it, then let us know if you which program you use for a sequencer, is xlights playing an LOR file, or did you convert it to xseq and how did you convert it (xlights, light elf, etc).
But to answer your basic question, the only real difference I've seen is the 2012c/2012d version gives you the ability to send your end channel on each universe--2012b didn't.