These tires need to be replaced at 10 years MAX from the DOT date. Period. End of discussion. Full stop. 7 years is the max for mounting. 10 years from DOT is EOL. Or you risk death in a roll-over. Condition, storage, tread, appearance are all completely and utterly meaningless. You buy NEW tires and you keep them for no more than 10 years if you like breathing unassisted by machines. When these fail they delaminate and the sidewalls get chewed by the rim and the asphalt. Unless you pull over immediately they will appear to have ZERO sidewall. That will occur in 1/4 mile of driving at 5 mph once the tire is deflated. It indicates nothing about how or why the tire failed. It failed from rubber deterioration due to age. Nothing more.
These are the general Army guidelines and what units with experience Motor Sargents will stick by regardless of command trying to say that weather checking is "cosmetic" - that's how soldiers get dead on US freeways in peace time.