Well, yeah, it's "disconcerting". I spent a good part of today trying to figure out where my players went. Of course, the answer (while illogical) turns out to be much simplier than I had considered. I should have consulted the boards earlier. Would have saved me a couple of hours of frustation. At least everything is now salvaged, I can delete the 1961 data from Catobase (a nice feature) and hit the ground running.
Needless to say, I'll be ready for the 1962 expansion coming up.
I'm not sure why this happened this way. Nor am I certain I would understand it if someone explained it to me.
Since this IS a sim-based game designed for (among other things) historic simulation across mulitpe seasons, you would think an expansion draft feature would be part of it. But, editing exported CSV rosters DOES work. So, I can't complain really about anything other than my own inexperience with the game.
Thanks again for the constructive input!