Hey Crin, don't know of this has been mentioned before but I'm pretty sure there's a glitch with sims who had Painting skill maxed before Seasons patch, just like gardening. Only in this case, it's connected to snowman building. No matter how many snowmen I build, I NEVER discover any new styles apart from the classic snowman. I must have built around 300 so far (not exaggerating, I play my collector sim with needs on static).
The reason I'm saying Painting skill is because when you build a snowman, there's a paintbrush icon on the action, kind of like when you're painting on an easel if you have Extra creative trait.
P.S. Found a solution to that though: as long as somebody I know can craft the other snowmen, I can tell them to start a specific snowman, then cancel their action and have my main sim continue. He never gets a notification about discovering a new snowman style but he does learn it and can craft it afterwards. :)