Policy periods rarely align with the calendar year. A policy might run July 1 to June 30, or start mid-month on the date coverage was bound.
Because Form 941 is filed by calendar quarter rather than by policy period, the two calendars have to be reconciled at audit. A policy that begins partway through a quarter touches five calendar quarters rather than four.
Why it matters at audit
Pulling payroll for the calendar year when the policy runs on different dates makes every number in the submission wrong, and is one of the most common reasons an audit is returned.