So why does the Schengen-visa tag still remain viable? Almost all the questions about Schengen visas (including singular visas) appear with the Schengen-visas (plural) tag. I think one tag's sufficient.
@David I had pending edits adding "schengen-visa" to two questions and the tag was then recreated. I don't have enough reputiation to mark it as a synonyme of "schengen-visas".
But I have added suggestions to those questions changing the tag to "schengen-visas". The edits have been accepted so the old tag doesn't have any questions a.t.m..