The most complex data set that we used in this article is the HPBD [LINK: https://www.cerl.org/resources/hpb/main **]. This is not an integrated metadata unit (such as the ESTC for example), but rather a collection of various bibliographic collections with varying amounts of data with issues of duplicates and the like. Thus, all the analysis of the HPBD need to be executed with additional caution, although we have validated our key observations by ensuring that similar trends are to be found in the other metadata collections that we use. Thus, we can rely on the general trends that are apparent in the HPBD. However, the more specific the analysis becomes, the more careful we need to be. One general feature of the HPBD when it comes to the question of format, along with the earlier noted sharp rise of the octavo, is the relatively large proportion of folio books (Fig. 1). It is worth noting that with respect to HPBD, the  folio format keeps a fairly large share of the total print area of published documents until mid-eighteenth century. We may notice a similar trend also in ESTC in Figure 1, whereas in SNB  folio seems to have been on a sharper drop for a longer period of time. Of particular places in HPBD, the large share of folio in Madrid and Brussels (Supplementary Fig. 1) catches one's eye.