I am replacing all 8 shims, dropping them two sizes (0.05 mm) and ordering new Honda parts. The wear on these shims was much greater than on my NX250's shim under bucket shims which I replaced at about the same mileage. With that bike I reused the shims that I could. With this bike I am not sure if the shims were sourced in Thailand or Japan, but, I will have new Honda standard 7.48 mm shims to replace the originals (no reuse).
The CB500XA's chain is DID, made in Thailand. A lot of people had to replace their chains at 10-15 K miles. The nuts and bolts on the bike are frequently over-tightened in manufacturing. I am adding anti-seize to most of the running gear, but not in the engine. The point is that some of the parts are not the quality expected from Honda, nor is the assembly.
BTW, I am replacing the spark plugs with iridium plugs while I am in there. You have to pull the fuel tank and take out an electronics tray that lives under the tank to get to the spark plugs on my bike. Is the Rebel 500 easier to access?