[gregpark]

Originally Posted by masraum

Seems it's more a "when" than an "if", but I suppose it's possible that folks could slip through the cracks.

I wonder if there's any sort of timeline after which the IRS snoozed and lost. I assume there is not.

According to the American Bar Association, the IRS will usually audit the "last 3 years" but in certain circumstances can go back an additional 3 years (6 total).
https://www.americanbar.org/groups/business_law/resources/business-law-today/2017-august/irs-can-audit-for-three-years/
But

It's a question of if. It's a voluntary system. The IRS audits thousands but millions don't file. The agency relies on scare tactics for compliance but generally runs it like a business. If there are assets and enough money to go after they could pursue. Many have told them to "take me to court" and never heard from them again. If one hasn't filed for years and goes to the IRS before they come to him it would be advantageous. The IRS has agencies within and you don't want the collection guys coming for you. A non filer could simply backfile claiming minimal earnings and get away with it a long a there's no 1099 paper trail