The open button at bottom is now standardised.
The original system was direct pneumatic control with the buttons to open so easy to have on both sides, retrofitting electronic control and duplicating and getting them communicating on ~35year old stock less easy. (following what was done on the SN 455 a decade ago and works well)
The 800s have the open button on top so it doesn't appear to be standard. It certainly confuses me. Back in the 1990s I'd reach for the top button and hold it in as the train stopped. The the doors would open as soon as they were released by the train crew. Now I have to look which way round they are.
Anyway, with regard to 317s, I took my 3 year old for a ride the other day. We went on a few unmodified units. Then we went on a modified set and he said "Daddy, someone has taken the buttons!" Also, despite the shiny new buttons, they retain the feature that you have to hold the button in to open the doors, rather than press and release. I'm always astonished by how many people cannot cope with this and stand by the doors looking helpless. Are they all first time travellers?