Is offline dictation officially supported by Apple?

I cannot seem to find any official documentation on this. This is what I have found so far using not-so-reliable means:

• Voice to text used to require an internet connection prior to iOS 9
• In iOS 9, Apple experimented with offline dictation for certain devices
• In a later revision of iOS 9, Apple removed offline dictation.
• Apple re-introduced Offline Dictation in iOS 10. I have checked this on about a dozen iOS 10 devices. The ones with A9 processor show this option and the ones without don't.

But I would like to get some official documentation on this before telling our clients that iOS now supports offline voice to text.

According to https://support.apple.com/en-us/HT208343

On iPhone 6s or later, iPhone SE, and iPad Pro, you can dictate without being connected to the Internet. Earlier models of iPhone and iPad require an Internet connection.

So you are correct that devices with A9+ processor can use dictation offline