"Length is not very important in evaluating quality of corks. There is very little difference between the effectiveness of a 1.75" cork and a 2" cork in preserving wine. Long corks are chosen over shorter corks largely because of their asthetic appeal---the loud pop when you uncork the bottle is appealing"
I was once told that as cork was quite expensive a winemaker did not bother with too long a cork if the wine was to be drunk fairly soon or was not of the best quality.
The length of the cork was, therefore, a mark of the quality of the wine.