This is fairly normal Lab puppy behavior.
IMHO, four months is too young for doggie daycare. It is mostly a free-for-all. There are what, 2 - 3 people watching at least 20 dogs? Yikes! I have two Labs and when I take them to some sort of a group play situation, it's pretty tough to keep an eye on both of them. So, basically, your puppy is probably often not being shown the correct behavior because those people cannot be at 20 places at once. Sometimes he is, sure, but I can guarantee you that at least 80% of the time he's not.
The key is supervision and redirection, not being allowed to get to that place where he's being too rough.
If you are having a playdate, keep an eye on your puppy. BEFORE things get to a bad place, using a toy or treat and holding the puppy's collar (not dragging the puppy by the collar) tell the pup, "let's take a break" and lead him away for a little time out. The key is that the puppy is not in trouble, he is simply taking a break so he does not reach the point of over-stimulation. Also, is the puppy collar conditioned as in he's been taught that collar grabbing is good? Most puppy classes cover that.
He will mature and the corrections will mean more to him and he'll most likely heed them. You might want to have playdates with mature dogs that give firm but fair corrections. In my experience, female dogs are pretty good at this. I would nix the doggy daycare until he is mature.