I thought it used to be a single O-ring and then they went to 3 to over-engineer it.
No?
The original was two o-rings, the redesign was three. There were other changes in the redesign, and I’d say the redesign was excellent and would probably be extremely unlikely to fail.
Browse through this PDF to see the redesign.
https://www.nasa.gov/pdf/553082main_Shuttle_Lessons_Learned_Buzzard.pdf