Kalamazoo made a variety of systems for filing, referencing etc. The safe could be a holder for any of these systems I suppose.
I shall ask you all a question. There is a small prize if anyone can get the correct answer before the end of the month. A bank where I did some work held the account for the British Legion poppy fund. It must have been an odd account- there would have been loads of deposits in November and probably 1 transfer out each year. It was in the Kardex system somewhere. What do you think they had it referenced under? Was it P for poppy day etc?
The problem was that without the name under which it was filed, it was impossible to find the account number, and without the account number, things were impossible.