Apple Photos Cocoa Error -1 when trying to export photos

So that is why they are not in your backup library.

If you've deleted them more than 30 days ago, so they are no longer in recently deleted, then they are gone, and not recoverable from the cloud.

The only other thing you could (if they are not stored esewhere - check social media etc) try to do is recover the previews from the library (if they are there). They will be lower quality, and possibly smaller.

Right click the restored library, and select show package contents. (DO NOT CHANGE ANYTHING IN THE LIBRARY - that will damage it and possible render it unopenable)

Look for a folder called resources>derivatives (naming may be different in earlier versions of MacOS)

Copy (don't move) that folder to another location on your drive, then look through it to see if you can find the preview version of the missing images. Filenames and folders will be random collations of letters/numbers. It might make it easier to browse them if you import into a new empty library.

Hi

That suggests the origninals/masters for those images are not available in the library.

If you have been using "show in finder" it suggests that you were not copying images into the libray, but leaving them on the hard drive where they were when you imported them. If this was the case, then backing up the library does not back up the images. If your whole drive is backed up, you'll need to restore the images separately.

How did you lose the library in the first place?

Do you have "copy items to library" under "importing" in preferences.

If you select one of these images and look at the info (CMD-i) does it show you the filename? If so, you could do a finder search for that image to see if it is still on the hard drive.

Hi

Do you (or have you in the past) have "optimise storage" turned on for your photos library?

This will also mean that full size originals are not in the library - being stored only in iCloud.