I downgraded from Catalina back to Mojave w Cataline. With my Mojave vers I cannot open my catalina vers of phlibry. How do I know if I have more pictures in PhAl than in my Photos file. Is PA just a rearrangement of photos from my Photos file? ?

Do you have a backup of your boot drive made just prior to what you upgraded to Catalina? Maybe Time Machine or a clone of the drive.

If you do then restore the iPhoto library from the backup made before you upgraded to Catalina.

If you're running a "managed" library

you don't need to save the source image files after they've been copied into the library. To do so would be to take up twice as much disc space as necessary.

jacchan wrote:

Thank you so much for replying so promptly. Unfortunately I did not do anything special to save my drive before I upgraded to Catalina. 1- I am now much more aware of the dangers when one upgrades instead of installing a new copy.

I have saved my photos in my photo folder which I have no trouble accessing in any version. My concern is that I don't remember if the photos I put into the photolibrary came only from my photo folder or whether I transferred photos from elsewhere so that there might be photos in the photolibrary that I have not saved in my photofolder. 2 - Do you know if photo folder is the only source from which you can download photos into photolibary?. If so, I do have my photos and won't have to worry about accessing the catalina version of photo library.

1 - I've never installed from scratch when I've upgraded to newer systems and have never had a problem.

2 - you can import photos into a library from any location on your drive, from an email, a website, a camera or phone. They don't have to be in the Pictures folder to import into a library.

Do you not have any backup of your hard drive? That's like driving without a seatbelt. You don't need them until you do. If you don't enable some sort of backup strategy you'll lose your data for sure. Because there are only two types of hard drives: those that have failed and those that will fail eventually. The easiest backup strategy to enable is Time Machine with an external hard drive.