I know at least one man who "failed" ADT (Lupron) and was thought to be "castration resistant". In fact however, when he got his testosterone measured it was 87 when the target number for his ADT treatment was 20. So he wasn't castration resistant at all. His problem was that the Lupron wasn't doing the job of bringing down his T level. When he added Casodex his PSA came down again.
I recommend that everyone on ADT get their testosterone level tested along with their PSA. Make sure that the drugs you're taking are doing what you want them to do.