Can a reference (not self) be over-cited?
Can a reference be over-cited?

Assuming you are using in-text citation, it is necessary to cite the reference in-text every time you use information from it.  So, there is no upper limit on the number of times a reference should be cited.  Increase the number of citations until there is no ambiguity, and then stop.  40 times is not that many.
In most styles each reference is only listed once in the reference list.