Tag filtering is only used for the duplicate target post, not the child post.
Q&A for students, teachers, polyglots, and anyone interested in the techniques of second-language acquisition
select top ##TopItems## parentPost.Id [Post Link], count(childPost.Id) [Dupe Links] from Posts childPost inner join PostLinks childPL on childPost.Id = childPL.PostId and childPL.LinkTypeId = 3 inner join Posts parentPost on childPL.RelatedPostId = parentPost.Id inner join PostTags parentPostTags on parentPost.Id = parentPostTags.PostId inner join Tags parentTag on parentPostTags.TagId = parentTag.Id and parentTag.TagName = '##TargetTag##' where childPost.PostTypeId = 1 group by parentPost.Id order by [Dupe Links] desc