Snow White was released two years before Wizard of Oz

I'm aware of the releases, the code didn't get used until the 40s but lasted right through to the Reagan era, it was also spurred an investigation by the NIS for the Navy in 81 looking for "Friends of Dorothy"

Dahl told a newspaper reporter that there were many gays serving at the base, which spurred the Navy to launch a purge of what they presumed to be a massive network of homosexuals at Great Lakes. In the course of their investigation, NIS agents made a startling discovery – that homosexuals sometimes referred to themselves as “friends of Dorothy.” This code term had originated in the 1940s and 1950s and referred to Judy Garland’s character in the film The Wizard of Oz. Ever since, gay men had identified themselves as “friends of Dorothy.”

The NIS, however, didn’t know the phrase’s history and so believed that a woman named Dorothy was the hub of an enormous ring of military homosexuals in the Chicago area. The NIS prepared to hunt Dorothy down and convince her to give them the names of homosexuals. In gay bars known to attract military personnel, Dahl learned that NIS agents were asking pointed questions about someone named Dorothy. When one unfortunate sailor acknowledged he was gay in order to get out of the Navy, NIS agents sat him down and told him that they knew all about Dorothy. What they wanted to know from him was how to find her. The sailor, who was too young to know the code, was baffled.