Say you are looking at the open era from the perspective of someone in 1982. You see the 80% career mark being reached pretty regularly every 3 years or so. You think it is a common thing for the top players.
Connors broke that mark in 1974. Then Borg in 1978 (or rather 1977 when the DC record is included). Then McEnroe in 1979. Then Lendl in 1982. And they never dropped back below that mark through their careers.
Then this regularity is broken after 1982, and there is 25 year wait until Federer reaches that mark again in 2007, followed by Nadal in 2008. It looks like Djokovic will break it also this year.
Similar thing with single year percentages above 90%. In the 16-year period from the beginning of 1974 to the end of 1989, such percentages occurred a total of 13 separate times -- almost every year. Then there is a 14 year hiatus until Federer does it again in 04, 05 and 06. Then Djokovic in 2011.
What to make of something like this is not clear. In the 70s, 80s and 00s, the best players of each respective decade got there. Not so in the 90s.
Were these anomalies due to the fact that they had stronger competition in the 90s, or was it because they were less dominant?