They were all from 3 different locations in the same local area (Chicago) not too far from each other. Two of the locations were in the northwest side of Chicago (near Irving Park and Harlem) and my current location in Wood Dale, IL just west of the O'Hare Int. Airport.
Like DavidEduardo pointed out DXing the AM band (or SW for that matter) was much different in the past. It was much easier to log new stations. The noise level in those days was much lower as well.
There were Chicago area based DXers (and members of CADX) that had higher totals in their log books than me.
How far did you live from WSBC, WCRW, and WEDC? I was always amazed at how strong they were out by the old WJJD tower site near Greenwood Ave. and Ballard Rd., especially since they all operated at the legacy mimimum efficiency for Class IVs/Class Cs to protect WJOB 1230.
Why did Olson Electronics have a map for DXers showing different frequencies in different neighborhoods?