The CP71C is an annual reminder notice. If you have a tax balance the IRS hasn't been able to collect — often because enforcement was paused, a prior installment agreement lapsed, or the account is in Currently Not Collectible status — the IRS sends this notice once a year to keep the debt on your radar.
What the CP71C doesn't say loudly enough: the balance is larger than it was last year. Failure-to-pay penalties and statutory interest compound continuously on unpaid IRS balances. A $20,000 debt that sits unresolved for five years can easily become $35,000 or more.
The IRS has 10 years from the original assessment date to collect. That clock — the Collection Statute Expiration Date (CSED) — is still running. But so are the programs that can reduce or eliminate what you owe. Offer in Compromise, penalty abatement, and Currently Not Collectible status are all available to qualifying taxpayers regardless of how old the debt is.