I am curious about your comment "even if that's not what it's really called".
Here is an early Kardex, and it is labeled as such in the lower left corner. Kardex has been the name or part of the name of companies tracing back to Rand Ledger founded in 1898, which were closely associated with the development of the index card as a common business data storage device. While Kardex 70 years ago made the warranty index cards for Porsche, today it is still active:
https://www.kardex.com/en/