a) isn't meant to insinuate that the positive test was false, just that he was no longer taking them as evidenced by the 19 tests he subsequently passed
b) his story was plausible, but highly unlikely. I was over the top with that one back when I was a bigger homer than I still am to a degree. But even then I wasn't saying it meant his story was true, just that it was possible.
c) that's PFF's hilarious excuse