I got an answer through search to this question, but the last answer, by Points Scrounger, is from 2008. This quote from a 2006 answer Points Scrounger gave explains the policy in more detail so I've quoted that instead but the general concept remains the same between those two answers: "A note about one-visit-per-month joints: you get credit for each partner on the first visit per month per partner; if you dine using your Priority Club card on the 1st of the month, and use an airline-linked credit card on the final day, that's perfectly okay. You can also split a tab between two partner cards as well on the same visit, which can be very useful if you are trying to fulfill more than one promotion."

Since I've seen nothing in this forum to contradict this longstanding answer, I'm assuming this policy remains in place--and kicking myself if my assumption is correct for not previously registering for mileage in programs other than AA for those places that I visit frequently but don't award in AA more than once per month simply because I like the restaurant and the miles are a bonus.

It had been long enough since this question was answered, however, that I thought a status update might be helpful.