So I've frankly found it easier to just file an extension every year and in Sept check my tax wage & income transcript to see what exactly the IRS got, and then file. Like one year an online wager site had provided the IRS with multiple w-2gs for horse race winnings of like $12 (yes, twelve dollars) each that I obviously hadn't even thought about give it was so small, and they never sent me a copy (I have no doubt I was supposed to like download them online, but again, who would have thought to look after winning $12...)