[hindsightbias]

The A-12 was publicly announced in early 1964. It first flew in 1962. The X-3, F-104, B-58 had all flown by the mid-50s. If anything, airplanes have been much more pedestrian as function and form needs were mostly subsonic.

[stretchcat]

As far as I am aware, the A-12 was secret until the 90s, though the existence of the nearly identical in appearance and function YF-12's was indeed made public in the 1960s. But how many in the 60s would have recognized one if they saw it? Public knowledge and common knowledge are not the same thing.