Do you have some examples? There's a lot of content Letterboxd (or rarely) do not import on their website, from TV content, to pornographic content to video content (sports, plays, compilations, etc.).

The entry that inspired this post was this one, and I have a few of my own creation, including Mundije, Gajen Nad, and Home Safe.

"Hollywood: Lights, Camera, Blasphemy!" is marked as video:true and Letterboxd doesn't import these entries. For the other ones, you should send an email to Letterboxd and ask them to import these entries manually; the automatic import does not always work.