The gap is between the file and the date
The strongest argument for a certificate system is not storage. Shared drives are good at storage, and a well-run folder is genuinely better than a badly-run system. The argument is that a certificate is not a document — it is a document plus a validity period plus a set of jurisdictions it covers, and a folder can only hold the first of those three.
So the other two get written down somewhere else, and from that moment the team is maintaining a join by hand. Every join maintained by hand drifts. It drifts slowly, invisibly, and in the direction that costs money: a lapsed certificate looks exactly like a valid one until someone checks, and the invoice that went out untaxed in the meantime has already gone out.
What a folder is still good at
Retrieval, if you know what you are looking for. Familiarity, because everyone already has one. And no procurement conversation, which is not nothing.
The point at which it stops being adequate is not a number of certificates. It is the first time two people need to answer the same question about the same customer and reach different answers — which usually happens well before anyone thinks the volume justifies a system.