"Hmm... no, time contraction doesn't seem to work, either. There's been a Christmas tree in each season so the best one could do is move the episodes around a bit [Huh]"
You can do anything you like, naturally, but it still can work -- how do we know that something memorable happened every Christmas during the first 4 years? Maybe there was just (unthinkable as it seems) one Christmas where absolutely nothing unusual happened! (unbelievable, isn't it?) So that six years was as possible as anything else in the show, which gives you a lot of latitude. My advice is just to ignore it. That works pretty well, too.
Nan
