On examining this 1876 Puerto Rican stamp, I see that counterfeits of the overprint exist. A closer look makes me suspicious.

Under the magnifying lens, the ink of the overprint and cancel look identical, as if they were applied at the same time.
Any thoughts?
This is part of what I call my 'Just because' collection. Stamps I keep in a separate binder just because I like them, so if it's not authentic, it's no big deal. Could even make it more interesting.