For several years when I was a child, we had a friendly tuxedo kitty. We had him neutered, so we KNEW he was fixed.
One day, he disappeared. We figured he was gone for good ... then a month later, he showed up again! Yay! The other cats were all cool with him, dog seemed to know him (she chased strange cats), and he moved right in and seemed to be his old self, albeit with a few new quirks in his behavior.
One of those quirks was spraying, which he'd never done before.
So we hauled him off to the vet to see if he had a UTI or any health issues.
Vet said, "Neutering him will help with the spraying."
"... but he is neutered."
Nope. Not neutered. And, as the vet observed, they don't grow back.
The second tuxedo cat was with us for several years after that. He got neutered in a hurry, though, because of the spraying.