Hi,
A fascinating recurring subject!
I think that in post #10, by Stephen Hand gives us a strong clue ;
http://swordforum.com/forums/showthread.php?t=84055
My own view is that in all probability rapiers did see combat during wars, just as knives did, but were not the weapon of choice and were used on account of dire necessity, for lack of anything better being on hand, rather than efficacy.
Cheers
Chris