Why can't I install an app (says "could not be found")? I just got an iPhone SE. I did a backup from my 4, then told iTunes to restore the new phone from the backup.

It said there were a bunch of apps it couldn't install because they cannot be found.

As just one example, Access RPN is on my 4, shows in my iTunes under "My Apps", but without art. When I go to the iTunes Store link, it says "Downloaded" so I can't redownload it.

How do I fix this?

EDIT:
I found an Apple page that says to do this I need an iTunes backup, AND a phone that's not set up. So I erased my SE and tried again. This got many more of the apps installed and their data recovered, but some still aren't working. Access RPN, my example app, still does not work.
Ok, in iTunes on the computer, it says "Downloaded". But on the device itself, go to

App Store -> Updates -> Purchased -> My Purchases

and select the "Not on this iPhone" tab. That shows all apps that didn't get transferred. Click the cloud icon to download them.

This even preserved the apps' data, because I had done a backup first.