In the late 60s Chestnut was under the gun to cheapen production. So starting in the late 60s you started to see a decline in production quality. My Prospector was right at about 68. What you see is: 1. Asymmetrical thwarts and thwarts not finish sanded on the underside, 2. One steel nail holding rib to inwale, 3.poor quality varnish (linseed oil based so the finish yellows). Then later maybe spliced outwales. Or rectangular profile outwales (not rounded over—Ed Haynes told me about that).
Integrity of form and general quality of wood was still good. Ed Haynes had at his store his own late 60s Prospector, which was good for a complete trip up the MacKenzie.