Here is a more complex version of the query that finds posts which had given tag at some point in the past: Posts which had given tag in the past. The new query also contains LastActivityDate.
The query has to look in two tables, which I did using inner join / maybe somebody more familiar with SQL knows whether there is a more efficient way to do this.
I have noticed that there currently exist tags surfaces (with description "A surface is a two-dimensional topological manifold. The term can also be used to describe a smooth surface, depending on the context." and 145 questions tagged) and curves-and-surfaces (with description "A surface is a ge...
Some merge/syn suggestion:
curves and surfaces both into curves-and-surfaces (one might want to keep them separate but then one might remove the latter)
Just in case some of those tags gets deleted after this discussion: curves-and-surfaces tag-excerpt, surfaces tag-excerpt. (Tag-wiki is empty for those two tags. The tag (curves) has completely empty tag-info - not even tag-excerpt.)
When I look at list of tag synonyms I see there a pending synonym rsk-correspondence $\to$ robinson-schensted-knuth and François G. Dorais♦ is listed as the creator. You can also see that this synonym is still waiting for votes on the corresponding page.
I know that regular users can suggest syn...