What does one call a group of similar courses where only one can be taken for credit?
A couple of universities that I've worked and/or studied that described the courses as having equivalent content.  So, the prerequisites for an upper-level course might be listed as "MATH 344 or equivalent content."

The reverse descriptor also came up sometimes.  For example, the degree requirements for a given major might include:  "Four additional courses at the 500 level, of essentially different content."  Another school used inequivalent content for the same thing.