Well what if the ditz that made your bottle was lazy, and possibly tossed some of a F-ed up batch in there? This is a common practice, as a yellowish tint on PVC fitting indicates this. In such a case your bottle is going to be weaker, versus that of one undergoing all the correct procedures.
Obviously, it comes down to ones standards. I personally don’t do things with a 20% safety factor, I would at least strive for a 100% or if not more. Once again what is wrong with 'safer' materials such as PVC/ metal? I know we may be stuck in this rut of looking like white trash, but I mean spend a bit more money to ensure safety.
"Coke bottles are rated to about 150psi plus they don’t frag" ~judgment_arms
What the hell? Where did you get such a figure? As clearly there is no pressure rating expressed on the bottle itself, and I think if there was such a number, Id think it to be out of the 'regular' persons means of gathering information. Wow, talk about pulling stuff out of your ass... [I know I sound I like a asshole, (Yeah the one your pulling stuff out of) but don’t throw out bullsh*t figures, for some random user to pick up and from such result in injury.]
As in the case MrCrowley mentioned, it appears that the incident was as a result of manufacturing error. This is exactly why safety factors are imposed. Although as much as it is tried to be avoided, you simply cant prevent such chances by imposing higher safety factors. You can significantly reduce the chance, but not eliminate it. The same exact reason why we here in the hobby suggest member to impose there own safety factors, and abide by ones given.