why doesn't icloud backup service restore text messages

A friend of mine with an iPhone 6S running ios 9.1, accidently deleted a single text message. She does regular iCloud backups. Since there's no way to restore an individual text message, she restored the entire iPhone from the latest iCloud backup. After restoring, ALL text messages were gone. Apple tech support doesn't seem to have any idea as to why, but the last tech we spoke with admits that the data should be there.

For those who would respond to this by saying, "iCloud backup is not supposed to back up text messages", I would like to point out that:

1) When she purchased the iPhone 6S a month ago, the sales person in the Apple Store initiated a restore from iCloud backup and all of the messages including iMessage, SMS, and MMS messages were immediately restored without any problems.

2) The following link from apple tech support does in fact say that messages are included in backups

iCloud: iCloud storage and backup overview

With that in mind, does anyone know why my friends text messages were not restored by iCloud backup?

Thanks in advance.