Our old diving club had a Chinook rib and it was definitely Hypalon as we carried out some repairs on it. The tubes were original and I believe the ribs were all made locally to me (Cheshire) on a farm?? Originally they made SIBs, then progressed to RIBs and even changed some of their earlier SIBs to RIBs or so our DO assured me about 20 years ago!
A while back a Chiorino company rep (they used to make Hypalon fabric) told me that if you hold a flame to an offcut of Hypalon fabric it will char where as other stuff PVC and Polyurethane will melt. (you know I think I will put that to the test tomorrow)
Could make for an interesting write up on an insurance claim form....
Oh and glued seams does not indicate Hypalon