Wrong.
† First checked bag free
From
https://www.aa.com/i18n/AAdvantage/earnMiles/beyondTravel/creditDebit/citi-platinum.jsp "For benefit to apply, the Citi® / AAdvantage® account must be open 7 days prior to air travel AND, reservation must include the primary cardmember's American Airlines AAdvantage® number 7 days prior to air travel. If your credit card account is closed for any reason, these benefits will be cancelled. Eligible Citi® / AAdvantage® primary cardmembers may check one bag free of charge when traveling to domestic destinations on flights marketed and operated by American Airlines, or on flights marketed by American Airlines and operated by American Eagle Airlines, Inc., SkyWest Airlines, Inc., ExpressJet Airlines, Inc., Republic Airline Inc., or Chautauqua Airlines, Inc. These benefits will not be available for travel on codeshare flights booked with an AA flight number but operated by another airline. For the Citi® / AAdvantage® card, up to four customers traveling with the eligible primary cardmember will also get their first checked bag free of charge if they are listed in the same reservation. Waiver does not apply to overweight or oversized bags. This benefit cannot be combined with any existing AAdvantage® elite program benefits, including any waiver of baggage charges. Please see aa.com for baggage weight and size restrictions. Additional terms, conditions and restrictions may apply. Applicable terms and conditions are subject to change without notice."
You seem to be correct, but I vaguely remember otherwise. Possibly the AA agent on a recent flight out of Philly told me that when checking in as a reason not to get free bags. I won in the end, but it was a hassle.