I can understand that, but he could have filled in with better material. For one thing, he dropped that character, whose name escapes me, who was the computer genius in mid story and never mentioned him again.
I had a friend years ago who wrote for two major publishing houses... she had a great technique. We would all sit around while she described a character and we had stacks of old magazines. We’d turn through the pages to come up with the person we thought would ‘look like’ the person she had outlined. Then she’s take the choosen picture and put it on a cork-board. Then rinse and repete. That way when she mentioned on page 30 the eye color of a character - she had already mentioned she didn’t have to spend an hour flipping through pages to use the right color on page 155. Same with a character who ‘gets lost’... as you point out - you see his face on the cork board - along with his eye color etc. and think ‘what happened to him’... When writers are young they can get away with doing things by memory - not so much when they get old.