We recommend using a different certificate for each of your templates. This is to make sure your Passes don't group at the same level instead of stacking.
Plus there's been a bug (discutable feature?) in the Passbook app since iOS 6.0 when passes with different icons share the same certificate: the Pass icon that appears on the lock screen may not be the correct one.
We provide every CaptainPass account with a few certificates for testing purpose only. You are not allowed to use these certificates for production passes.