That's nonsense. Michelin would not take the risk of putting sub-standard tires on the market. Worst case scenario is that Costco may, from time to time, be able to get tires with minor cosmetic blemishes having no impact on their performance, durability or safety. Check the tires that you buy at Costco and save the bucks.

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Reno

'93 300E 4Matic
'98 Nissan Altima
'00 Yamaha Road Star Silverado