The backdoor in the EC DRBG algorithm was detected but never leaked because to actually open that back door required a key only the NSA had, but that key itself

The backdoor in the EC DRBG algorithm was detected but never leaked because to actually open that back door required a key only the NSA had, but that key itself never leaked. Only the NSA could decrypt streams that used this PRNG. To everyone else they remained undecryptable. So it's not a counter-example and your amusement is misplaced.