I have been testing myself for the last month. I've taken about 30 at-home tests. I started passing them after 21 days, but then failed tests at 32 days and 42 days. In between I was passing with first void of the day. So, it is possible to test clean and then provide a dirty sample afterwards. However, given that you have been clean over 5 months, I think it'd be VERY unlikely that you would provide a dirty sample at this point. Also, since it has been two weeks since you tested, don't you think your P.O. would have contacted you if there was a problem?