tzdata does not remove timezone names.

If the 'Asia/Manila' timezone changes to the 'Asia/Shanghai' timezone, the old timezone will still exist, but a rule will be added to indicate the change.

The tz name here is a specific name in the tzdata database, so it's quite easy for that database to never remove any entries, but to rather deprecate them or link them to new ones, if appropriate.

Yes and then you'll have old source code that still uses the old names to indicate time-zones and newer source code that refers to all the newest names of time-zones.

If the timezone name changes, chances are I no longer want to meet at 6pm in London in 10 years' time without double-checking a few things.

Honestly, this applies to the entire rest of the thread too.

No? If the UK decides to stop doing DST or synchronize when they do DST with North America I still want to have my meeting at 6pm local time. Not have that meeting be 5pm or 7pm for some reason.