I have a 2009 fifth wheel and the date codes are on all tires. I think they are only stamped on one side of the tires though.
Often when tires get older, they are put onto the vehicle with date code inward when they get older. A piece of clean cardboard and a digital camera set on closeup will give you the numbers you are looking for.
Recently I read an ad for a motorhome. Ad said new tires. When I asked how long they had it... five years or a bit more... did you buy the tires.. No. So the previous owner put them on then.. Well they were in good condition when we bought it. Hmmmm,