Never heard of a date code on a belt, so I wouldn’t trust that. Don’t purchase anything until you do a couple of tests. As long as you have the fenders and seat off, I’ve got a couple of dumb questions to ask. First, is the belt going to the tranny tight or snug? Second, with the unit off, can you move the tensioner arm by hand to exert more pressure on the belt? Third, when you press down on the brake pedal and then release it, does the tensioner arm always come back to the same spot? Fourth, when you tried to drive the unit while jacked up, did the belt run smooth and tight, no slipping? Why do I want to know? 1. A belt that is not good and tight will slip under load. 2. If you can move the tensioner, it means you have a missing or broken spring or it is dirty and rusted at the pivot point. 3. Same as #2. 4. This would be the cause of a worn belt. If it was me I would replace the belt before I stuck money into a tranny.