It's sort of known that coating of the bulbs, and even those "filters" eventually fade and make those bulbs unsafe. Filaments are fixed, so it really can't glow any differently. But these changes really happen gradually, unless something happened and they were scraped off.
I dunno.... a fresh bag of Dektol is about 10 bucks these days? I just practically gave away my old safe light. You may want to ask around here and see if anyone has one for sale. I know a guy in Atlanta selling basically his entire darkroom in classified. You may want to look around and contact him privately.
If you were closer, I'd just give you some of my Dektol for testing but 400 miles is a bit much for a quick drive. I'm near Orlando.