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Making sense of a manuscript corpus as large as that of Ibn Ṭūlūn can be tiresome. In particular, since his autographs are today dispersed in libraries in Syria, Lebanon, Egypt, Turkey, Germany, England, Ireland, the Netherlands and the United States, and the relevant institutions offer very diverse degrees of information about the manuscripts in their catalogues. Yet, these catalogues are obviously a central source in establishing any manuscript corpus.Things get especially irksome when one wants to make sense of the collections of the Dār al-Kutub (for guidance to its collections, see this review) and the manuscript center of the Arab League (GAD) in Cairo. Access to microfilms at Dār al-Kutub is comparatively easy if rather slow (due to the limit of three items one may order each day); access to the physical manuscripts themselves, however, requires good connections and a lengthy stay. One might circumvent the Dār al-Kutub altogether by turning to the GAD, which offers an online catalogue to browse the selection even beforehand and allows to collect digital copies within the same day.The GAD offers access to the (partial) holdings of several important manuscript collections of the Arab World. Yet, therein lies a danger as well as new possibilities. The catalogue was apparently created on the basis of the individual library catalogues but their holdings were not compared to each other. What I mean by that: Several collections hold microfilms of manuscripts belonging to another institution. In the GAD catalogue, the same material artifact may thus appear several times. In some cases, doublets might be visible through an allusion to the original collection in the "subject" section but often enough it is not.https://researchblogs.cul.columbia.edu/islamicbooks/2012/08/14/digitalsurrogates/This is, however, not a new problem. With the spread of microfilm and microfiche in the early 20th century, collectors and scholars alike made ample use of these technologies, and, among others, the Taymūriyya Library (today in Cairo) and the Arab Academy in Damascus supplemented their manuscript collections by acquiring microfilms from other institutions around the world.These microfilms received their own call numbers, being treated somewhat similarly to manuscripts physically present in the respective collections. Even though this process is clearly important to the constitution of the corpora which ground our understanding of Arabic literature and book culture, to my knowledge no study has yet been dedicated to this important chapter in the transition from a living manuscript to a print culture (and hence to digitization). Yet, in the face of the ubiquity of the medium, we need a new "codicology" for  microfilms.To conclude with just one basic example, the integrity of a text in a physical manuscript is partly assured by the use of catchwords on the verso page of each folio. The text is bound to the materiality of the two-sided leaf of paper. In contrast, microfilm images present a surface to the viewer, which usually covers the verso page together with the recto of the following leaf. In order to assure that the following image actually refers to the following double page in the physical manuscript, it would require a catchword on the recto page.While this might seem a theoretical issue at first sight, the microfilm of the Ibn Ṭūlūn autograph manuscript Majāmīʿ Taymūr 759 is only one case where the addition of such catchwords would be really necessary. For about the first half of the files I bought from Dār al-Kutub, the slides only seem to be in the opposite order (fol. 100 comes before fol. 99 before fol. 98 etc.). Yet, around the middle, the confusion increases even more and it is painstaking to find out which image belongs to which work. Finally, about half of the texts ascribed to this manuscript by the latest print catalogue is completely missing from the microfilm.&#160;