IIRC, some of the Delco regulators had a temperature-compensating system built into them, but it was to increase the voltage slightly under hot operating temperatures. It's been close to 30 years since I did much work with generator systems on a regular basis, so I'd have to look up the specifics of your system to make an educated guess what's going on. Regulator points open and close several times a second under normal operating conditions, and they have a slight wiping action to help keep the contact surfaces clean. If any roughness develops on the contacts, it's possible for them to stick and cause the voltage to go up until the sticking condition corrects itself.
Jerry
