> The four-minute barrier was first broken on 6 May 1954 at Oxford University's Iffley Road Track, by British athlete Roger Bannister
> On 21 June 1954, at an international meet at Turku, Finland, Australia's John Landy became the second man, after Bannister, to achieve a sub-four-minute mile.
In 1955 Laszlo Tabori was the third person to break the 4 minute barrier. Then, in 1956, three runners broke the four-minute barrier in a single race.
This matches what I described, multiple people attained it once it was understood to be possible. It was linear up to the 4 minute mark, but the point is that records that used to be impossible are now humdrum once achieved.
