Yes, I'm sure about this....
Like the Theory of Natural Selection...and the Survival of the Fittest.
The bad ones are weeded out by excessive modding, abuse, disregard, lost parts, disrepair, natural defects, etc....
The ones that are left were good enough to keep and care for. The ones that compared favorably to years of newer basses being produced. They got played alot or were preserved well (either was a positive). Their growing value ensured someone would always maintain them very well.
And once the term "vintage" is applied to a particular guitar, it earns a permanent status which sets it apart from newer ones, adding to it's chances of remaining/or landing in the hands of someone who appreciates it and protects it's monetary worth.
Therefore, as years, decades go by,...the once reviled 70's Fenders will have been distilled to generally the very best specimens. And their reputation gradually rises.