Good catch -- and really, I find it to be quite foreboding in terms of how indomitable it is precisely because of the secrecy of the program.

"This was a secret treaty, allegedly so secret that it was kept secret from the Australian Prime Ministers until 1973."

This is indeed a trend, and I speculate that NSA (and NSA-like entities in the other 4 eyes/countries) probably communicate information and abilities to prime ministers and presidents of the respective countries very selectively.