Join Date: Apr 2009
Location: Bye Delta
Programs: AA EXP, UA Silver, HH Diamond, IHG Plat, Hyatt Plat, Marriott Titanium, Nat'l EE, Avis PC, Hertz PC
Posts: 16,614
You can also tell from the seat map. 8 rows of business class is the regular 789. 14 rows of business class = 78P with the suites.
If they moved your husband to row 14 and that was still in the business class cabin, that sounds like the 78P.
Browsing the flights offered for sale in November, it does indeed seem that AA20 is being operated by a 78P, at least on every date I checked that month.