I don't own many art books, but this was the first book, art or otherwise, that had its color plates attached in this way. In researching the issue, I see definitions
of "Tipped in" that refer to "pasted along the inner margin of the appropriate text page", but the color plates in the book I've got entitled The Moderns
by Gaston Diehl have the plates adhered to the page at each of the four corners
As you can see, the adhesive is beginning to fail at a number of points.
Is this indeed a "tipped in" plate, and if so, how common is the method of four-corner attachment?