@François Dorais: Concerning the tag geometry, there are about 500 questions with that tag which do not also have a geometry-related tag: https://mathoverflow.net/questions/tagged/geometry+-dg.differential-geometry+-mg.metric-geometry+-ag.algebraic-geometry+-gt.geometric-topology
If we take questions with that tag which do not also have a geometry-related tag as a measurement, they went down from 500 to 315 in those four years.