I came across this scenario today. I had an Intune app available but no assignment already. End user wanted an app. I added an available assignment to the group and ran a sync. I checked the pmp log and see the app I was working with but nothing listed as to what group it was assigned to or a info line of new assignment succeeded.
The pmp publishing service email doesn’t state new assignments but does for new updates/base installs.
So what would be really nice is the acknowledged of a new assignment group either in the pub service email notification or in the log.