If the condom gets so far as to expose the head, then it has come off completely and it is not going back on.
Hypothetically, if the condom was to slip off all the way to the head, then it is off. For it to be able to go back on down to the base is if it was stuck in her in the same exact position when it was on you AND you reinsert your penis in the exact way needed to reposition the condom correctly. Otherwise, you would have pushed it inside her. Make sense? Don't over think it, please.
but, im not talking about complete slippage, im talking about slipping to a certain point where the head was exposed and then slipping on back again near the base of the penis....
You have to be patient with us voluteers. We are not here to answer your questions 24/7. But really, no one can say with 100% certainty that you were safe. I have had condoms slip of of guys before and they always get pushed inside. Once that happens, then it doesn't go back on. I agree with Vance. Since the condom was on when you pulled out, it is not likely that the condom slipped off and went back on...on its own.
No i don't think it slipped off...if it did chances are high that it would not have been back on you when you pulled out. What would have happened is from the thrusting it would have come off all of the way.