They're taken off of U-18Chan, where they were posted in groups one comic at a time, but the file names have the sequence number in each comic at the front, and don't identify the comic in the file name for the most part. This is just a grab of all the posted files with no changes to the file names, so we have to sort them out by hand. Toward the end are the ones that were posted with the comic name in the file name.
for a while there I thought the artist may have been doing some kind of challenge to do nothing but first pages of a comic to see what catches peoples' attention and what doesn't.