Steve Ditko responds to a fan request about memories of the design for Spider-Man’s costume:
My work on Spider-Man was done in the early 1960s. That’s a long time ago to remember details especially, it was just another comic book art job. I’ve seen later reprint material that I did that I don’t remember doing. How far back can you accurately remember doing something if asked to remember.
You can see the letter for yourself here. That Steve Ditko has some nice handwriting, as well as some refreshing honesty.