According to Freight Cars of the Ann Arbor Railroad by Craig Wilson, that series was 100 cars, numbered from 500 to 599, inclusive, all of the same design and paint scheme, built by Greenville Steel Car Co. in 1964.
While originally purchased to haul cement out of Dundee, Michigan, most of them ultimately ended up hauling sand from Yuma, Michigan (northwest of Cadillac) to a Ford foundry in Brook Park (suburban Cleveland), Ohio.
-Fritz Milhaupt, Publications Editor, Pere Marquette Historical Society, Inc.http://www.pmhistsoc.org
90% of the time it's a safe bet, but exceptions occur when railroads dump a varied group of renumbered secondhand cars into a series. That doesn't appear to be the case here.
Fallen Flags has photos of AA 534, 548 and 563, all in the same billboard paint scheme (some more the worse for wear than others, but all the same original paint) - that's the other pitfall a modeler can fall into: where a unique paint job might have been applied to one or two cars and not representative of the entire series.
In this case, it looks like yes you are totally correct, this is a pretty typical solid series of identical cars. Probably something like AA 500-599. (I don't have a dated ORER on hand to confirm that range though and AA isn't my particular speciality.) I note some minor differences in the side posts at the corner of the body, so the prototype cars are built by a different builder, but very close.
Chris van der Heide
My Algoma Central Railway Modeling Blog
Ive recently purchased the Atlas PS2s for the Ann Arbor railroad. Unfortunately there is only 3 road numbers yet I would like to have 5 for a cement industry. The lowest numbered car is 520 while the highest is 581. Is it safe to assume all cars in between are in fact identical cars and a simple renumbering to any number in between would be prototypical? If not could anyone link an appropriate substitute?