jxk, not all O-rings have a shelf life. In fact, most of the O-rings we currently use haven't got any limitations.
In my environment, I will definitely stick to approved data and specifications. Why? Because I usually have got an ample supply of compatible and serviceable components. In another environment, it is only fair to deviate from such procedures using both experience and common sense. It is needless to say that any deviation should be documented and corrected as soon as possible.
What does actually frighten me a lot more is the worrying state of some O-rings I have removed. Let's say you remove some accessory and find at least one of the O-rings badly cut and towelled, wouldn't you wonder if this had already happened during assembly?