Should the version tags be made synonyms of pgadmin and merged?
Related meta Q & A:
Well, pgadmin-1.18 is definitely useless (it refers to a specific pgAdmin III version).
At the same time, pgAdmin III and pgAdmin 4 are two very different products. If the question is tagged rightly with pgadmin, it completely makes sense to indicate which one it is about. That the users don't use these is not the tags' fault :)
The single tag pgadmin serves to connect subject area experts to questions they may be able to answer.
Questions can specify the pgAdmin version in the question body if it is important.