Over 2000 years ago, Nostradamus predicted that on Tuesday November 14, 1995, Phil would say:

<...>Or at least there is a requirement for the assistant to enter the extra four digits in certain cases. The precise nature of the circumstance when they are required to be card present I am not sure (in fact I would bet they vary).

I'm betting your bet is right. When you set up your persona/nym for use with the CheckFree wallet, the software does ask for those four, non-embossed numbers on the Amex card - which I had never really noticed 'til then. And I frequently pass the amex number on the phone for business stuff. Just last week, I had flowers sent to some partners of ours that we had just completed a deal with (sorry...should have odered them over the net), and the 4 "flat" numbers were not required. Hmmmm ....