Jingles is advocating you re-add the fixtures to the same channel and see. DO THIS on a copy. Save AS before doing this.
In my experience, once you remove a fixture, the data behind those channels is gone. This wasn't all that long ago I was screwing around with that sort of thing to pointlessly see about moving fixtures around. I say pointless because I didn't think it out very well so my plans didn't work out. MY failure, not MyDMX failure.
May your luck be different.