I’ve probably had a lot of games where groups unexpectedly live or die.
The reason why we’re not dan players is inconsistency in some cases 
You make a misread here or there and your corner dies or some other group now has a ko for no reason etc.
I think in a lot of players play, there can still be some missing fundamentals for example, because we don’t have to have passed a test to say our endgame has to be at least X level and Tsumego needs to be at least Y level.
Probably pushing beyond 2d, 3d and so on that might be the case though.
Anyway in some of these cases the sekis only show up when the dame are all filled like
and it’s just a mistake of one player not to realise the aji.
Other players when behind might have resigned rather than fill in the dame, at least if they’re not actively spotting the aji. So that can lead to maybe an under representation of certain types of seki maybe.