I like one # for all certifications because it’s simpler… but then when someone wants to verify the certification, you have to make sure you filter by certification before you respond.
If you do multiple IDs for multiple certs, then the candidate has a raft of numbers to remember and document, and you have determine see which one to refer to when you correspond. Not ideal.
Their ID, whichever way you do it, should be good for the life of the certification, meaning the original and all subsequent recerts.
The recert date is the date the certification was issued. It is also the date on which the recertification was issued. You may choose to include a field, “Certified since 2014” or “Initially certified 2016” or whatever, but this is optional. Most people don’t do it because how do you handle gaps in certification?