Or in other words, is there an adjective meaning something "has never been repeated after the first instance"?
ODO defines unprecedented as "never done or known before".
For example, in the following sentence, is there an adjective I can use in place of "never again made" so to change it to "through 'xyz' efforts"?
The plot of “A Report to an Academy” is that an ape having shed his simian nature transforms into a human through speech and reaches the position he is at now by attaining the refinement of an average European through efforts never again made on earth.