ummm...then clearly, as has been mentioned a million times, your focus is on the wrong things. You're asking about Retro and you can't remember what you AGREED to about your children's holiday schedule. Your first post about it said "who knows for sure?" Well YOU are supposed to know.
Now you have to approach it with W that now that you've had more time to think about it you'd like to change the agreement. That requires a little more diplomacy. Perhaps you should think about what plans you'd actually like to make for the holidays, PLANS, Kevin, for you.
I think it's a bit telling that your major concern is that "it seems like she's having a blast." Not really about how much time you get with the kids. Who knows if she's having a blast. Maybe YOU should seem like YOU are having a blast. Maybe you should approach her with some wonderful things you wanted to experience with the children for the holidays, so you would like to arrange that.
Get off the pity pot, FORGET about Retro! and start making holiday plans. Get online and find something to do. Talk to your family about what they'd like to do for the holidays. You know what Moms do? They start planning this stuff NOW. Get involved in your own life!