I'm really surprised that you don't have to do any kind of re-assessment. In St John Ambulance, everyone has to be "revalidated" once a year, including ambulance crews, and the assessors will stop you from going out on duty if your skills aren't up to scratch. Similarly in IT, if you pass a Cisco exam then it's only valid for 3 years, then you either have to retake it or take a higher exam in order to keep that qualification. (I've sometimes thought that it would be a good idea to do that for GCSEs too - I've forgotten a lot of the French I learnt at school.)