How can I recover photos that won't export from a macOS photos library, can't be edited, and have no originals?

Hopefully this will serve as a more focused and generalisable version of [this question](https://apple.stackexchange.com/q/387121/175188) and [this question](https://apple.stackexchange.com/q/399027/175188) . - This isn't my system photos library so the photos aren't in iCloud. - About half the 12,620 photos in the library fail to export (Unknown error: -1), can't be edited (Cannot Start Editing: Photos can't load edits for this image.) and have no corresponding file in the Originals subfolders within the .photoslibrary package. - The photos aren't thumbnails, or at least Get Info reports full resolutions. - Like other people who've asked for help for this problem, the problem photos seem to fit a date range. In my case this is from the start of 2011 to about mid-way through 2015. - The same issues occur with my oldest Time Machine backup of the library so restoring from Time Machine isn't an option. - I tend to always keep my media libraries consolidated and, if the file creation date is reliable, I created the library in 2021. So it's unlikely the problem photos were simply never copied to the library in the first place and subsequently lost their references. I might be able to recover some or all of the originals from the people who took them. But, needless to say, I'm looking for a technical solution here. **Edit**: Merging duplicates brought the total number of photos down to about 6,500, but unfortunately nearly 80% of those are "problem photos".