IIRC, the phone system was modified in the 90s to allow multiple area codes in one geographic area.

As late as the late 1970s, in some areas, if you were calling a different number in the same exchange, all you had to dial was the last 4 digits. For example, if your number was 555-1212 and you wanted to call 555-1234, all you had to dial was 1234.