Beatles, Stones and Floyd albums can be frustrating due to the sheer number of pressings. For non-barcode releases, I just enter the matrix numbers in the search function to narrow things down. Of course, it could still pop several versions for cover and label variants.
If your pressing truly isn't in the database (it happens), you can add a version by selecting "edit release" then "copy to draft" and finally "add a release" that will copy over all of the details and you can change the relevant info (and photos if needed) and submit for approval. If you have a title that isn't in there at all, you can choose "submit a release" under "explore" drop down on the top menu (on the desktop version).
If someone else has a simpler way of adding a pressing to an existing title in the database, I'd love to know about it because I've input 2,000 titles from my collection so far and the way I've described above is clunky at best....