To ofxisfun : ) ,
are you sure that if my FI supports 2.1.x then I don't have to specify the card number, even if I'm NOT using "1-WAY OFX", but using the REGULAR credit cards statements download (with the <CCSTMTRQ> aggregate)?
or maybe your answer was just about the option of using "1-WAY OFX"?
I've checked with Amex. the don't support 2.1.x, just 2.0.3