[willy]

That is true, also you will find late boats that have soft transoms and early boats that are as hard as a rock.
The way a boat was maintained over the years makes the biggest difference. Some boats have bolt holes that are rusting and the owner never sealed them, some installed engines and did not do a good job on the bolt holes etc. some installed electronics or transducers along with thru hulls and did not bed the parts correctly and allowed water to seep in over the years.
If those boats are sealed up right, especially if they are a trailer or rack stored boat they will last indefinetly