IMCA does not state any expiry as far as I aware.
As with everything else IMCA, it is up to employers/companies as to what they are willing to accept. IMCA is not law, it it s a trade organisation that has set up a defined set of standards. Companies can choose to follow them, or ignore them, it is completely up to them.
Training schools may decide to issue a certificate which runs out after 1 year, 5 years or never. The certificate is as "valid" now as it will be in 100 years time.
It is up to the companies what they wish to accept.
e.g. they will expire if the company decides they wont accept them after a certain time.
