I have both 2015 and 2019 Photoshop elements on my computer. The 2015 has 11,000+ images and the 2019 has 12,000+.I assume that the 2019 version is correct. But, all of my albums are missing. I have had the program dormant for some time. Now have to transfer to a different computer because of other problems but certainly would like to have my albums back. Looking fresh and help. Thanks.
The only way to recover the 2015 albums into the 2019 catalog is to convert the 2015 catalog. This will ignore the missing one thousand files (probably more recent). So, with 2019, use the converted catalog and try to re-import all your files, which should ignore already present files in the converted catalog. Check if this brings back the missing files in the 2015 catalog.
Now, you can use the backup and restore process to move your photo files library and your converted catalog to a new computer.
For more safety, I would also create a full backup from the 2019 original catalog.