This has happened to me twice now, and possibly a a third time now-
The clearance items seem to be oversold a lot.
But just in general their website does not protect against overselling.
Fanatics seems to protect against overselling much better.
So if you're buying as a gift and timely and can't risk a refund due to overselling, I'd suggest using fanatics.
Otherwise, if you're really in it for the prices, seems lids has better clearance sales.
Another roundabout bonus from this that I got: if there is a coupon dealing with a minimum purchase and you only want one shirt that is not on clearance and is below the minimum, you can buy that one shirt plus a few clearance items and there will be a chance the clearance items will get refunded to you because of overselling and voila you have your original choice of shirt but at a discount without meeting the minimum purchase requirement