I couldn't find quickly the source I found last summer that described
the process of Tip-in in bookbinding and book preservation...but here
are two definitions that show the source of this idea coming from
tip on, tip in, tip up http://www.redmark.co.nz/glt-z.htm
To incorporate a single sheet, plate, endpaper or section into a book
by applying a narrow strip of adhesive to its back margin and sticking
it to the back edge of a section.