The city's pension office apologized for the error and contacted the pensioners to offer advice on how to get free fraud and identity theft monitoring in the wake of the oversight.
Still, many affected pensioners weren't happy, U-T San Diego reported Friday.
"That's the most important number you could possibly ever have in this country," said Dennis Webb said, a retired police detective who said his identify had already been stolen once. "You can wind up developing a case that would burn a judge's ear off."
Those affected by the error are among the oldest retirees -- who left their jobs before 1996 and collect a lower pension than many other municipal workers do.
The city greatly increased pension benefits in 1996 and again in 2002 -- but not retroactively for workers who had already retired. They receive annual stipends totaling $14,244.
Facing a deficit of $37 million this year, largely driven by a municipal pension payment of $275 million, city leaders moved to reduce pensions by 25 percent across the board. The move was aimed at more recent retirees receiving the greater benefits but affects the smaller pensions as well.