When adding a 1973 movie a search on its title "female vampire" fails. Alternate titles for this movie also fail. I've tried "les avaleuses", "erotic kill" and "The Bare-Breasted Countess". Searching on imbd finds it, id 0069745. On occasion med fails on a search but has always found the target with an alternate title. Not with this one.
For adult titles to show up when searching, it's required to be logged in on IMDb. On the "IMDb Settings" tab in Preferences you can provide username and password which will be used when searching on IMDb.
Go try to search for an adult title after logging out of IMDb in your browser, and you'll see ;-)