What the number is for

The email said: the green one I bought from you, it has started receding at the base, what were you keeping it at? Attached was a photograph of our own listing card, still in the tank.

Because the number was on the card we could open the record, read the parameters it had been held at three years ago, and answer in one reply instead of ten.

That is the entire argument for permanent addresses. Not provenance as marketing — provenance as the ability to answer a question three years later.