Forget the control of Records clause in ISO - do what make sense for your business.
Your log book sounds like you are tracking the certificates (which is actually controlling product) - the question is how much do you want to track. Do you need to know exactly what is on the certificate that is in the customers hand, or do you just need to know they have a certificate - and maybe some further info like an expiry date etc. ?
How are the certificates produced? Are they a report from a Database, or something like individual documents?
As for version control of the certificate 'layout', I am in favour of it, particularly if the certificates are individual documents. It is a way of ensuring that the certificate has been created in the current approved format using the approved information (this is something I am dealing with currently).
Summary of what you need to control:
Product - the certificate: You need to in your case, be able to identify product - so the certificates need a unique identifier like a serial number, or a combination of Issue Date & Customer, some thing that identifies that particular certificate.
Documents: The policies, procedures, work instructions etc used to conduct the testing and produce the certificates.
Equipment: You need to ensure that your testing equipment is calibrated obviously for your buisiness, but also the supporting systems like databases, spreadsheets etc are producing the correct output.
Records: You need to keep records that show you followed your approved procedures to produce your final product (the testing results and certificate). You also need to keep records that show your equipment is working correctly (calibration records and testing records of the databases and spreadsheets etc.)
There are other supporting systems like Management Review, Audit and CAPA that will have their own document and record requirements for an ISO system.
I'm starting to ramble a bit here.