[Quoth]

I spent 20+ years designing & implementing Relational databases. The difference in how tags work vs editing a Series name or an Author name isn't inherent to using SQL, it's a design decision. It could create a new entry in the tag table rather than change the entry, that naturally all the titles use. I've not seen this behaviour on other columns. There may be sound logic to it. I don't really use tags and thus I haven't thought about it.

Editing an Author or Series only changes the title being edited, though perhaps I've never ONLY edited the case and maybe that behaves the same.