Perhaps we are missing something else, Enlarger size, these were sold as:

These fell into:
35mm (828/126),
120 - Medium Format
Large format 5x4 - 10x8

It's no coincidence that these are the formats Peter mentions above, and used by professionals and serious amateurs. Formats like 828 & Instamatic were never taken seriously despite Kodak's attempts make high end camera's, 126 fit SLR's went the ame way as later APS SLR's people preferred 35mm.

In addition film sizes were categorised by camera manufacturers as well as technical authors in books & magazines.