A belated thanks for your reply! Apologies for my erroneous diagram - it was done from memory.

I think the only other place I noticed horizontal segregation remaining in T3 is a couple of gates at the end of Pier 5 (Gate 36 I think), where one gate crosses the flow of another before reaching the arrivals level.

It makes sense that 13 would be departures only, though that wasn’t my original guess, mainly because I wrongly assumed more gates were affected by the issue I described!

And I saw the operational challenges in effect - it seems to cause a huge pain. In the case of my arrival, the GA for a closing flight was pressuring the staff member responsible for the doors to let passengers through, while staff for the arriving flight (mine) was pressing to be let through because the jet bridge was wet. Most other airports with this type of segregation (LGW South Satellite, EWR, MEX T1) have at least two routes by which they can send passengers, whereas this pier of T3 only has one route. I noticed CDG 2F has special revolving doors to get around this problem, which let an equal number of passengers through from each flow with each rotation - I’m amazed they aren’t more widespread!