You can't restore local copies of apps that you backed up using iTunes in iOS 9? But you can download older copies of apps on a first gen iPad? That's weird if that's what you are saying. I was able to download older apps on my 1st gen iPad about a month ago.
Edit:
Are you sure it stopped working? You can't download an older version of an app on a non supported OS unless you either previously downloaded a version before on a compatible device or used iTunes and bought the app on a computer.
Edit 2:
Apparently you still can download the app to your computer directly using iTunes but you can't back it up to your device.
Edit:
Are you sure it stopped working? You can't download an older version of an app on a non supported OS unless you either previously downloaded a version before on a compatible device or used iTunes and bought the app on a computer.
Edit 2:
Apparently you still can download the app to your computer directly using iTunes but you can't back it up to your device.
https://www.google.com/amp/www.macworld.com/article/3125509/...