Happened with sailboats. Years to be particularly concerned about are mid-70s during the energy crisis. Changes in resins and layups to save money during that time resulted in a lot of "iffy" build quality depending on the builder.
Also varies by builder and ownership of said builder. Builders are always looking for ways to save money and will change layups and hull design to reduce laminate. Some worked, some didn't.
Late 60s and early 70s boats are generally built like tanks because they didn't know how much glass was needed. They thinned out considerably through the 70s and had mostly sorted out by the 80s. I tend to avoid boats built between 74-76. Sticking with well-known builders tends to work better.
In the end you need to do research and know the model of boat you're looking at. For example, I will *never* touch an O'Day 30 despite being very happy with an O'Day 22 and like the O'Day 37.
SV South Paw
2000 Hunter 340
South River, MD