Credit Period vs. Compliance Period
The "credit period" is the 10-year period during which the owner claims its tax credits. It began either the same taxable year your building was placed in service or the following year.
The "compliance period" is the 15-year period during which you must follow the tax credit law to keep your site in compliance. It starts the same year the credit period does but lasts five years longer. This is because you must maintain compliance for 15 years, even though the owner claims its 15 years' worth of tax credits over just 10 years.
Remember that you must maintain compliance for an additional five years after the owner stops claiming tax credits—that is, after the credit period ends. If you don't, the IRS may take back credits the owner already claimed but doesn't deserve.
If your building's tax credits were allocated after 1989, you'll also have to deal with an extended use period that follows the compliance period. But, during the extended use period, you need to comply with only those restrictions that appear in your extended use agreement—not the tax credit law. If you don't comply with these restrictions, your state housing agency may take legal action against the owner. But, because the compliance period has ended, the owner's credit will stay safe.