As ever, it varies depending on the person doing the checking. However, yesterday, going to Pier C (Thai flights) they seemed to only allow bottles that clearly said 100 ml printed on the label. I had a label less bottle which was in fact 100 ml, it was not allowed in my case. It is true that they normally don't inspect the duty free bag, so one might get away with reusing it, but it would not be correctly sealed, of course, so it could cause problems if they spotted it.