This common graffiti from the WWII era, similar to the American “Killroy was here”, was known to the British as “Chad”. Unlike “Killroy”, “Chad” would normally be accompanied by a slogan saying “Wot no …?” (the ellipses being filled in with the name of something missing or, as so often in Britain during the war, in short supply).
I don’t know if “Killroy” was a rip-off of “Chad”, or vice-vera (or if they each arose independently).
Anyway, the point is that in the WWII era in Britain, “Chad” was clearly considered a common enough name or nickname to be suitable for an “everyman” character. It wasn’t something new 25 years before the OP in 2004.
Names do in and out of fashion in a cyclical way. When I was a kid, names like “Emma” and “Emily” were old-lady names. Now, some 50 years later, those names evoke young hotties. In between, they probably became quite rare for a while. (I would check this, and check Chad and Trey etc. too, with the Baby Name Voyager, but it doesn’t seem to be working.)