The files with numbered names contain one tune or dance description. The file name is of the form "PPN_Title.abc", where PP is the 2-digit page and N is the tune's number on the page (usually 1, but some pages contain 2 tunes). Initial articles are omitted in the file names, and are uncapitalized in the T: lines, to help software to a decent job of alphabetizing. Also, the double bar lines are sometimes darker than in the book, to make them easier to spot. Initial repeat symbols are added to a few tunes (those without pickup notes), to tell the reader that it's the start of a measure and of a repeated section. Feel free to "fix" any of these changes in your copy if you like, to whatever convention you prefer.
Also, staff breaks are not always the same as in the book. This has been done mostly to make my "proofreading" copies compact. You might like to have fewer bars per line, displayed or printed with larger notes, especially if you or a friend has vision problems. One of the useful things about ABC notation is that there is a lot of software that can format it for display or printing however you like.