My brother in law is a big chested guy and we rode the "time warp" at Frontier City (back when that ride was at the park). It had over the shoulder restraints and a seat belt, but the seat belt wasn't long enough to fasten to the OTS restraint. The attendant (older gentleman, not a kid) told my brother in law that it was okay, don't worry about the seat belt, he wasn't going to fall out....which he didn't, thank God. But I could see a lot of the attendants not knowing there could be a danger.
The New Texas Giant had a similar issue where the ride restraint said it was closed, but because of the size of the rider, the restraint didn't keep them in the ride (seat belts were then added to all the RMC coasters).
Jay