There's no need to be consistent with Psycho IV. That movie -- like all of sequels to the original, really -- was mediocre at best.
was a fine sequel and a top notch thriller in it's own right. Nothing mediocre about it whatsoever. Psycho IV
was a poor movie though I don't blame Anthony Perkins, Joe Stefano or Olivia Hussey. I put it all on Universal hiring noted hack Mick Garris. Garris couldn't direct his way out of a 7-Eleven parking lot much way a prequel to a Hitchcock classic.