Sadly I have no solid proof but Netflix did continue supporting the Original iPad (on iOS 5.1.1) using the old client for quite a while
Edit# NVM there it is, actual proof lmao https://vid.puffyan.us/watch?v=DVAZbsVvQqE it’s towards the end of the video but yea, the old client did continue to work in 2019
The way they got iMessage to work is by hiring a Foss developer who did something pretty amazing:
They reverse engineered the iMessage protocol and emulated parts of macOS that are necessary when registering an iMessage account on a device!!
https://github.com/beeper/pypush