I'm pretty sure UCI Rule 49 banning small wheels long preexisted 1996. There's little information on the web, but The Spaceframe Moultons describes the ban existing in at least the 1994 pamphlet (it's on google book search if you want to hunt: chapter 9). And certainly there's lots of stuff on the web claiming a near immediate ban, though with no specific date. Do you have any evidence to the contrary?