I've collected 6 Christmas Blizzards so far and just noticed that I'm missing the Brrrrrrrrr achievement which requires me to "Collect the Christmas Blizzard."
Some achievements will have been lost I'm afraid - to cut a long story short, we were doing some work on the Achievements database, when a query went awry and deleted the wrong data (we were trying to pry out some duff data as the result of a code bug). Normally we would have a backup, but in this case, it doesn't seem the table was backed up properly so those rows have been lost! Some of the achievements will auto recover (if they use a counter, the counter is separate, so the system will realise you should have unlocked that achievement and correct itself), for some it's not so easy, the item ones we can recover, but some of the others I can't guarantee.
I just spent all of my cubes on crates to get another blizzard, which luckily I did and it gave me the achievement. Let's hope that sneaky little bastard stays this time. And that I'm not wasting all of my time and effort on pointless ass achievements that won't mean anything once they're done as I only have one achievement left to get lol.