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 '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.