Last fall Ed Testa discovered something ominous about his past, a secret that had been kept from him for more than 20 years.

An unpaid parking ticket from 1988 somehow, someway, popped up on a Registry of Motor Vehicles computer when Testa went to renew his driver’s license.

“For 20 years there was never a problem when I renewed my license,’’ said Testa, of Marlborough. “then, all of a sudden, they tell me I owe this ticket that I don’t even remember.’’

A number of things can trigger an automatic hold on a license or registration renewal: missed child support payments; unpaid excise taxes; outstanding court warrants; Tobin Bridge or Fast Lane violations; citations for abandoned vehicles. but how could an unpaid ticket just reappear after all those years?

Testa said the $55 violation was from Cambridge, so my first call was to Susan Clippinger, director of the Cambridge Department of Traffic, Parking, and Transportation.

My hunch was that some intern had spent last summer entering scores of old tickets into Cambridge’s computer system, tickets that were printed before Clippinger’s department became tech-savvy. one of those rainy-day projects that finally got done.

But Clippinger’s department had computers back then, she told me. Testa’s ticket was entered into the system when it was issued on Sept. 28, 1988, the same year, coincidentally, that President Obama began racking up his infamously unpaid parking violations while attending law school at Harvard.

Testa’s ticket was reported to the registry after it went unpaid, as is standard protocol, Clippinger said. her department sent additional reminders to the registry for the next four years, records show. (State law calls for holds on license renewals if you haven’t paid a ticket within 21 days.)

“once someone has an outstanding unpaid ticket, and we notify the RMV to put them on hold, we assume the RMV does that,’’ she said.

Testa’s conundrum wasn’t much of a mystery to the registry. while it’s not well publicized, spokeswoman Ann Dufresne told me that it takes two unpaid parking tickets to initiate a hold on a license renewal, not one. (Or one unpaid parking ticket and one other hold-eligible violation, she said.)

Sure enough, Testa missed paying another parking ticket, this one issued in Gloucester in 2005. since he had renewed his license just a few months before that ticket was issued, and renewals are good for five years, it took until now for the hold to affect him.

In the end, Testa paid his Gloucester ticket, was granted a reprieve from Cambridge, and got his license renewed. Everything’s swell, except . . . he’s gotten yet another parking ticket . . . in Cambridge.

“Based on what I’ve learned, if I don’t get any more, it will just sit there for 22 years or so,’’ he said. “Only kidding. I plan on paying it.’’