TDmidget said it best.
I've used plenty of old stock vitrified wheels. The Federal Stock System stumbled on a trove of WW II era vitrified grinding wheels that fitted our large Mattison surface grinder. The boxes were dusty but the wheels inside pristine. Everyone I used rang sweet and true and they were 40 years old at the time.
If they were used and had stale coolant dry in the porosities, there may be chemical voodoo that would attack the vitrious bond but, somehow. I don't see it happening. Remember, grinding wheel safety is one of those low probability/high consequence deals.
My advise would be use new old stock vitrified grinding wheels that rang satisfactorily but trash used vitrified wheels exceeding 5 years since their last use.
In my experience, resin bonded wheels are rarely used in general purpose machine grinding. You generally find them used in glass fiber reinforced cup wheels for angle grinders and abrasive saws, or in more refined applications like thread grinding, super-abrasives, form grinding etc. I"m not aware of shelf life restrictions applying to resin bonded wheels in unused condition of for that matter vitreous bond. I suspect the Norton caution is more liability avoidance/cynicaly self-serving (tell the customer to toss perfectly good wheels so we can sell them more) than advise based on impartial product experience studies.
As always in using grinding wheels, work safe, wear eye protection, replace guards removed for machine servicing, inspect/ring wheels before placing them in service, etc