american english - Present Perfect for the past?

I've come across the - more or less - following sentence in a book (American publisher):

"They have done it in the past"

I've always thought that "PAST" and "PRESENT PERFECT" can't go together. The proofreading for the book is generally rather poor so it might be a simple mistake. Or there's more to it, is there? Like the PresPerf is there to stress completion? Or - aware of the US tendency to replace PresPerf with Past Simple - the author tried too hard and ended up hypercorrect? Or am I reading too much into it?