Lab puppy biting

Question
Took our 5 month old chocolate male Lab to the vet recently.
Had him neutered, a microchip put in, and his dew claws removed (breeder didn't do this for whatever reason).
He has been with me from the first day he came home at 2 months (I work at home) and plays with our 7 year old Lab female and other neighbor pets without any problems. He has
been to doggie daycare a number of times since age 4 months with no problems and does like to "mouth" human visitors, but never bites seriously.  At the vet, he did clamp on to a Tech after coming out of sedation and having several needles and the aforementioned surgeries done when they went to put him in a crate (not his own).  The receptionist
advised me of social training and local laws governing dog
biting (which was not her place) and I tried to explain to her (as if she would listen) that he was away from me the whole day, had pain from multiple surgeries, and was being placed in a strange smelling cage by strangers.  Am I wrong.

Answer
I really don't think so.  It is common advice that when a dog is injured, to muzzle it no mater how well behaved.  I would really think nobody should be surprised at a dog biting under those conditions.  

Yes, it would be best to train him out of mouthing people.  The only way to do so is to very consistently correct him for it.  At his age, it will take a while and many, many corrections.  If it was easy, you wouldhave already done it.  The best correction is to yell ouch, jerk you hand away, and walk away.  Losing your attention is a powerful tool.