Hi again, and thanks for your helpful reply.
Because the safe is over 20 years old, the serial number may not be in the same place where they put them today, on a sticker near the upper door hinge, with the model number. The underside of the handle was a good place to look and I would also check each surface of the safe on all sides, including the top and bottom.
The only way to recover a lost combination is by contacting Sentry through the site, below, but they will require both the model and serial number:
You can find Sentry's contact phone number on that webpage, too, and you can speak to them to ask where the serial number would be located on such an old safe, if it's not in any of the locations I suggested/you already tried.
I hope this helped and wish you much good luck with your safe!
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