The very first illustration in the first Terran Trade Authority book begins the unfortunate trend of pictures that contradict the text.
This, like most T.T.A. illustrations, existed before the book’s conception. It was Angus McKie’s cover for Dangerous Visions 2, edited by Harlan Ellison. In some cases the T.T.A. illustrations were personal works by the artists, who made contributions to the text (especially in the latter two books). So the images and text in the T.T.A. book may mesh better than in the original publication (for cover assignments, artists often pull existing works from their portfolio, even though they sometimes have nothing to do with the content of the novel).
But sometimes it’s clear that the picture existed first and the T.T.A. text was an afterthought. Here, for example, the hull of an alien ship in Spacecraft, 2000-2100 AD is painted with the letter “A” and several Arabic numerals. It also annoys me that this ship looks very similar to some of the ships illustrated by McKie in Great Space Battles, but those are identified as belonging to a different alien civilization.