If you go back to the manuals EMC and later EMD issued in the 1930s and the 1940s, most of them have an identifying bulletin number either printed on the cover or on the page inside the front cover. This is not part of the page or chapter numbering system, it is a distinct number assigned to that particular type of manual. This is particularly true of the manuals for the FT locomotives, it seems that every time they did a run of manuals for a particular railroad they assigned a new bulletin number. I have never seen any index or listing done of these, and am curious whether any of the other contributors to this forum might have seen a list?