Back last weekend, after both Citi and Barclay's had deferred me to AA (as according to them both, AA runs that program and they have no visibility or control over that), I got a pretty quick response from AAdvantage back and they said that Citi and Barclay's, as two separate card issuers, each have their own 10,000 yearly cap, and that specifically with one card of each it'll be 20,000 combined cap (they didn't clarify is it 10% or 20% to that 20K cap, though, and never responded to my follow-up to clarify that). That is, with multiple Citi or Barclay's cards it'd be still 10K yearly cap, but with one of each it will be 20K: 10K per card issuer. Clearly and unambiguously so said.
But, seeing the recent experience of others here, so does not seem to be the case in practice. May be that is why for over five days now no response back on my request for clarification w.r.t. is it 10% or 20% then until the 20K yearly cap...as they'd have to backpedal and say that it's not so after all.
I won't push them for it though and if they limit me to 10K yearly cap, will quote their own mail where it's unequivocally clearly stated that it's 20K cap (10K each card issuer), and that they never responded to my follow-up which would have been a perfect opportunity to tell me that they were mistaken in the original reply (if so was indeed the case - still too early to tell IMO).
Any more real-life experiences here for >100K mile bookings and both Citi and Barclay's cards, please post here and share your experience - is it really still 10K combined cap (5K each), or does it go to 20K as AA says it does/should.