Export previews script

I looked for and installed this script in order to recover a few images for which I lost the originals.

I followed the instructions and managed to get the script going.

It works.

However - and I have tried also individual pictures, one at a time - I can only extract a few of the pictures, which is disappointing after having been so close to my goal - about 10%.

And all those pictures have been uploaded in the same way and can be all can previewed in the same way.

Anything I a missing, here?

Thank you