Just Kidding I Found It.................look To The Left...
Actually, it's quite possible that you joined RX before September 2004. That "Join Date: Sep 2004" would appear on all RX veterans who registered before September 2004 (during the forum database upgrade) but most veterans have already checked & figured out when they really joined RX.
You can try to do a search of one of your earliest posts by keyword that you might remember. Then, a mod can help you confirm when exactly you joined RX and update your Join Date accordingly.
Cheers,
* CalvinTy