Last count was 50, wasn't it? I'm grinning here thinking about how you're going to handle at least 600 blocks and especially how you're going to lay them out to divvy up 12 at a time.
Are you going to lay each set of 12 in a stack and then just take one from each of 12 stacks, then the next 12, etc? Maybe you'll take one from every other stack.
Oh, that's not including the one that each person gets back. So, if you make 50 stacks, one of each person's own block (maybe with their return envelope) then make 50 MORE stacks of the other 11...
Inquiring minds want to know. Who knows, one of us might be doing this someday.