I think you should add the 100% tag to levels that require it -- for consistency with earlier challenges and because, like Clam's earlier point about the bold levels, it's a way of saying "this one's done, nothing more to do here".
Taxing 100% levels: 3 (required), 9 (required), 10 (direct drop glitch), 11 (required), 16 (previous challenge), 18 (previous challenge).
Mayhem 100% levels: 1 (previous challenge), 2 (previous challenge), 17 (easy; just place the blocker on a bridge, bash to release).