Steve:

Call Rewards Network to inquire about a missing dine. Splitting the bill is perfectly OK at unlimited joints. Give them the Visa info when they ask; at that point I'd advise them that I split the bill, so that this is separate from the AMEX charge that came through OK.

FYI - multiple charges at the same joint, on the same day, for the exact same amount are automatically rejected by the system as "presumed duplicate billing errors." If this is your case, now you know to vary the tip to get totals that are 25 cents apart for Priority Club dines (and 20 cents apart for all other partners). For instance, if I had a (pre-tip) tab of $36.22 I'd ask the server to put exactly $20 on one card (leaving a zero tip), and $16.22 on the other, adding the tip for the entire meal (rounded to the nearest 25 cents). In this hypothetical case, 15% = $5.43, so (in theory) add $5.53 to obtain 2 tabs that multiply neatly by 8x to squeeze out exact PC points: $20.00/$21.75. You get the idea.
Moreover, as a caution, I'd never leave exactly $15, but $15.20 (or $15.25 for PC Dining). I've had a couple of joints round my tab down a penny ($5.00 came through as $4.99) for some internal reason of their own.

Good luck and let us know how it comes out!

Points