The track surface is important and Landy had problems with that in his attempts at getting under 4 minutes. I think when he did go under the mark in Turku, Finland they kept lane one open and unrun on during the other events. I also recall Santee thought he had a really good chance to to go go sub4 in California one time, but it rained right before the race. I almost think he thought his way out of a sub4 in that case according to how the book retells it.
Bannister broke the mile record in 1954, but people don't relaize how long the previous mark had stood. The two guys who went back and forth with it in the 40s Haegg and Andersson (sp) got so close without getting it and then they were declared professionals. The training that Haegg did was very light like Bannister. He did not like running long distances nor did he like running slowly. Both of them used fartlek and made it a training tool for future runners.
I believe Andersson when he ran a 4:01 record mile was hampered during the race because the starting pistol cap that was discharged as the race was started fell onto the track and it lodged in between his spikes. He felt he would have run under 4 minutes had that not happened. History certainly would have changed if he did.