Everything you need to know here:-
https://www.caa.co.uk/Commercial-ind...l-certificate/
You've got your parlance slightly wrong, if your certificate has not lapsed then you need to re-validate. Renewal comes whenever your medical has lapsed. After that date, the time period elapsed depends on the course of action you must take.
- If your certificate expired more than 2 years before your attempt to renew it, the examiner will need to assess your aero-medical records before carrying out the renewal examination
- If your certificate expired more than 5 years before then you will have to follow the same process as for initial issue