Jdub928 wrote: I have hundreds of photos/videos on my iMac in iPhotos that were taken by a digital camera pre-iPhone.
Me, too. And I have scans of slides and prints pre-digital.
How did you try to get these pictures to iCloud? Did you look at iCloud.com to see if the pictures were there?
I would use Mac "Photos>File>Import" to import the pictures to the local Mac Library. If they are in folders, you can have Photos keep them in the same groups. (You may have to clean that up a bit, afterwards.) Then Photos would automatically upload those pictures to iCloud Photos, if Mac Photos was connected to iCloud. Then iCloud would automatically download those pictures to any iCloud connected devices that didn't have them.
What did you do differently?