Have an expiry period on a certification itself, much like inductions. E.g. First Aid cert entered in the Cert manager is given an validity period of 1yr. So any first aid certs uploaded for people automatically alert based on ValidFrom date entered. I know there's the ValidTo date on each uploaded cert, but this is pretty error prone and it would be a good reference for people to know that the cert is only valid in our eyes for 1year before they need to renew.