18 is nicer of the two .......in the 4.5 VG+ range.  Has nice appeal and could grade higher for many but does have a 1 1/2 inch spine split at bottom of spine and dark oxidation shadows on back cover edges.  Edges of all pages show some foxing stains, but pages are supple and otherwise creamy.  complete with covers and centerfold attached well at staples.  Front cover has great cover colors and decent gloss.

21 is a lower grade copy in Fair range with back cover coupon clipped out that leads to other tears and spine splits.  Lots of general wear at edges including small tears or creases.  Cover is only attached at top staple...centerfold at both.  Some small edge tears of pages in 1st half of book where book has been fanned through the pages.  Still decent looking front cover.