It's very rare when a movie is missing from the IMDb.
Example one of the movies that I have and cannot find on yours or IMDb database is P.O.W. the Escape with David Carradine
This movie is already on the IMDb, here's the page:https://www.imdb.com/title/tt0091713/?ref_=fn_al_tt_1
It's also in Coollector but with the title
Behind Enemy Lines [Attack Force 'Nam]
With the next update I'll add the aka "P.O.W. the Escape"
and the media is a vhs tape.
In Coollector, you go to that movie and you'll see that the "existing videos" box knows 3 VHS of it. You click yours or the one wich is the closest, then you click the button "Add as owned".
You said you need a imdb number I looked at your samples you posted in this forum and when I clicked on the movie in your sample what came up is a prime video page with that movie
What you describe is very weird, please tell me where I can find that forum page you talk about.