The inspection cycle is a customer calendar you already own
Pennsylvania requires an annual safety inspection, which means every customer a store has ever delivered to has one predictable moment each year when they must take their vehicle somewhere and pay somebody to look at it. That is an unusual gift. Most states give dealers no equivalent recurring reason to be in touch.
The stores that treat it as a calendar rather than as walk-in traffic capture the visit, the declined work, the tyre and battery conversation and eventually the trade. The stores that do not are effectively donating an annual touchpoint to whichever garage is nearest the customer's office.
The emissions county changes the message, not the schedule
Some counties add an emissions requirement to the safety inspection and others do not. It is a trivial detail and it is exactly the sort of detail a customer notices when you get it wrong, because they deal with it every year and you apparently do not. Branching the reminder on the registration county takes an afternoon and makes the whole programme read as competent.