The rule and the event are separate
“Two per year” is a rule. The dates of the prior services are the events needed to apply it. A payer response that supplies only one side cannot confirm whether the next service is available.
The year may be calendar, contract, or a rolling number of months. Those definitions produce different answers near a boundary.
Codes can share a frequency bucket
A periodic exam can sometimes share a limitation with another exam type. Imaging groups may combine codes that look separate on the schedule. Verifying one code in isolation can miss the shared limit.
The result should name the applicable family, the stated rule, the returned history, and the next eligible date when it can be determined.
Do not invent the missing date
If history is unavailable, say so. Using the practice chart as a substitute can help planning, but it is not proof that another provider did not bill the benefit.
The best next action may be patient confirmation, payer follow-up, or an estimate that plainly states the unresolved history.