Tax bloopers big already thanks to stimulus checks

Didn't get a stimulus check? Think you deserve more than you got? Got one but think it's taxable? Or do you have a very limited memory and have no earthly clue what a "recovery rebate credit" might be? (A credit for people who discovered their 2007 rebate checks in the bottom of their recycling bins, perhaps?) Chances are, you're one of a whopping 15% of tax filers so far this year making an error on your return.