Condoms?

Is it okay for condoms to be a bit loose at the tip. Its tight at his base and when you pull the condom back you can tell theres no holes or tears. But when he starts going theres like a bagginess at the top sometimes. Does this mean the condoms slipped or does the condom actually have to come off for that? We put it on correctly and examened it before and aftwler sex and it looked the same. Are we using them right? Thanks for the advice!