I keep seeing that explanation about "them" not knowing how much fiberglass was needed. Is it really believable that "they" would build with this new material without at least having some basic understanding of the strength of said material? I mean come on.
I think you are right that 'the Industry' caught on pretty
quickly to the structural properties of fiberglass. The engineering
that went into the early Cal boats like the Cal 20 & 24 has clearly
proven to be pretty spot on fifty years later. In most cases, any
structural failures in these boats is due wooden support structures
rotting away. There are of course many builders, past and present,
that have substituted over building with massively thick lay ups
for solid engineering.