When the front and back endpapers show the same information or picture, the fly leaf of each endpaper can be used to construct one complete endpaper. The constructed endpaper is usually attached to the front of the text block.
Separate the fly leaf from the pastedown. If the hinge area is weak, the fly leaf can be separated by gently pulling it away from the pastedown; if the paper in the hinge is in good condition, cut it away.
Check the alignment of the two fly leaves. If there is an overlap, trim back the two parts until they meet correctly, If there is a gap in the two pages, it can be filled with Japanese repair tissue when they are hinged together.
Hinge the two halves together, then use link stitch to attach the endpaper to the text block. Sew the endpaper to at least three adjacent signatures