As you said, DB plans vary. It really all depends on the company/agency's plan documents.
For example, ours don't follow age+service. It's minimum 55 years of age and minimum 30 years of service to avoid penalty. 54+31=85 doesn't cut it. Neither will 57+28=85. The 30 years service is also a hard limit for early retirement for our plan. If I leave with just 29 years of service, I'd have to wait until I'm in my 60s before I can take pension. Heck, retiring at 54.75 means pension is just 64% instead of 70%. That's a 9% increase for just one measly quarter.
Again, please note, the 65% is if I delay claiming pension to 55 so that's without penalty (just 2 years less service). If I claim pension at 53, pension is 57%. For my specific DB plan, sure, it's just a 23% difference (70/57-1). However, I have seen plans with much steeper early retirement penalties (e.g. 1.0-1.5 multiplier before normal retirement age, 2.0-2.5 for normal) so I'm not really all that surprised with the OP's situation.