Do you know how the filtering works with https in the URLs? I tried this against my own site (https://findlectures.com/), but I don't get results unless I take the "s" out, despite Google displaying it that way.
You've got 70 pages indexed there, so you should see some results once you make a search.
Update: 39 results now for searching "a" at https://lectures.googleblade.com/