Current status of deprecated tags: There are 954 questions with deprecated tags. (On August 25 there were 1000 of them.)

abstract-algebra has 347 questions, 205 if we eliminate most frequent top-level tags from this area. 123 with no top-level tags.

(The link to the last one is too long to fit into character limit for message in chat - but you can simply take one of the links at the end of this post and replace abstract-algebra for the tag there.)

discrete-mathematics has 182 questions, 86 of them without co.combinatorics tag, 47 with no top-level tag at all.

geometry contains 426 questions, 265 of them without common geometry-related top-level tags, 158 with no top-level tag at all.