A lot of shims don't have numbers. But there is an obvious up side and an a down side- I believe one side is harder. The only reasonot reject a shim is if it is really scored or worn.

Valve adjustment is a matter of math.

You need a micrometer or a measuring caliper. Since you have a handfull of shims you might have the ones you'll need. Check the valve clearances

If any are off, note by how much. Remove that shim. Measure it with the caliper. Do the math. Measure the ones you have at hand. If you've got the right one --- lucky.

You can usually get a garage that services Volvo's to sell you the shims you need.