Goitein left roughly 27,000 index cards in his files. They are organized in two categories. More than 7,000 describe the contents of a single shelfmark or document. The other 19,000 focus on topics (e.g., children, clothing, family, food, the weather).
Below is a more detailed guide to Goitein's index cards from Oded Zinger, “Finding a Fragment in a Pile of Geniza: A Practical Guide to Collections, Editions, and Resources,” in Geniza Research in the Twenty-First Century, ed. Jessica Goldberg and Eve Krakowski, special issue of Jewish History 32:2–4 (2019).
[Goitein's] laboratory constitutes the best semiavailable database for the documentary Geniza. [But] some guidance is needed before it can be used efficiently. [...]
The best way to get acquainted with Goitein’s index cards is just to dive right in. One quickly learns to read his hand in Hebrew, English, and Arabic, and most of the abbreviations used should not pose particular difficulty. It is, however, important to keep in mind that, reflecting the trajectory of Goitein’s study of the Geniza, there are often two sets of cards for a given subject, one general and one related to the India Book.
This is the index card for the אבן אלגאזפיני (Ibn/Ben al-Ghāzfīnī) family of cantors, roll 19, 154, drawer 20 (10C), 523. Goitein recorded nine documents (an additional document is noted on the back of the card) with a short description, noted where one of them was published, and proposed a dating for two others. Notice how the card reflects his ponderings over completing a lacuna in one of the documents and over the meaning of the family name (based on place, based on occupation, a November 30, 1969, letter from the biblical archaeologist Abraham Biran, and references to the geographic dictionaries of Yāqūt [= yaq] and Ibn Duqmaq [= Duq] and Ibn al-Ukhuwwa’s Maʿālim al-qurba fī aḥkām al-ḥisba). Incidentally, the reference to ENA 2738.12 is a mistake for ENA 2738.22.