Do bond lengths vary across molecules of the same kind? I only have superficial knowledge of chemistry, and today I found out about bond length for the first time. For example, on Wikipedia it says that all C-C bonds of benzene have a length of 140 picometres (both C-C and C=C, I think). But is this exactly true for all benzene molecules? 

Or does bond length of C-C vary slightly for 10 molecules of benzene? Is 140pm an average distance for a million molecules, or each and every benzene molecule has bonds of length 140pm? Is this a fundamental and unvarying length of the benzene molecule, so that a different length cannot possibly occur?

I know that during studies of the bond length in the laboratory, each individual measurement has a slight error. I'm not asking about that.
The atoms within a molecule are not stationary, but are constantly vibrating, twisting, etc. Thus, the value given for a bond length between two atoms must be an average. Specifically, the average distance from the nucleus of one atom to the nucleus of the other is what constitutes the definition of bond length.