Is this normal?

I have a 4 month old puppy and he seems to have some teeth missing in the front of his mouth. My friend knows the guy who gave me the dog and was saying that he was told that someone had adopted my puppy but brought him back and apparently they were possibly abusing him. Now he’s a very friendly dog although he’s come a long way. He was very nervous when I first got him and he seemed kind of depressed but happy to be around people. He has slowly warmed up and now he’s very happy but the teeth thing is something that I was worried about especially now after hearing that other information. Is it possible that someone pulled the teeth or is that normal for a dog this age to not have all of its teeth?

*He has seen the vet and I didn’t ask the first time because I assumed that this was normal at first but he has to go back again for his next shots and I will ask them but I’m just genuinely wondering what could have possibly happened