Winter tires 245-60r18 instead of 245-50r20. Will costco install as r18 not there on car door placard?

Winter tires 245-60r18 instead of 245-50r20. Will costco install as r18 not there on car door placard?

Costco says they will do it only if it is mentioned on car door placard or car owner manual. I am not able to find it in online manuals.. has anyone gotten these installed at Costco? Or how to show proof that these are compatible ones?

Thanks