Interesting. Monorchid would imply only one testicle, but worded the way it is, it could also imply just one was removed and he didn't attempt to even find another. My understanding is that if there's an undescended testicle, the surgery to remove it can be quite invasive. Do you remember if there was an unusually large incision or if there were special instructions for the recovery time after surgery?
I suppose it's possible the operating vet couldn't find a second testicle, undescended or otherwise, and therefore assumed Gryphon was monorchid?
Any way you can call the clinic where it was done and see if there are any notes in the record as to what happened during the surgery?
Geez, I hope you can get this figured out and it's not cancer.
Our babies worry us so much...