My husband went in and was tested for his sperm count (?) which is what he was suppost to do like 6 weeks or 20 ejacualations after he had his vasectomy (he didnt because he was sent to Iraq when the war started). Had he went in when he was suppost to, we would have found out then there were still live floaters in there (almost certain it did not heal itself together as it is very rare), and not be faced with the situation today... our 7th child. my 9, 8, and 6 year old are mine and my ex's. He has an 8 yr old from a previous marraige also. Our 4 and 3 yr old are ours together, and this one. wow, I am 30 weeks and still in shock. Our families dont know still, and I made him go in for testing because I wanted to make sure toilet seats really can't do it to ya! LOL
Anyhow, yes it can happen, likely not though, after a SUCCESSFUL vasectomy! I blame it on Army doctors in my case!! haha Just be sure to tell every man who has it done to go back in for his check up!