This is where we are going to have to agree to disagree Nam. I'll tell you why (with what you call one of my u-know-what slaps.
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Joe Stephano, who wrote the first film decided to dismiss parts 2 and 3 (which followed all the continuity laid in the first film, added to it, and then put the genie back in the bottle by the end of part 3 as not to sully the first film. Perkins and the others wanted no errors or glitches that would do such). The only sullying they did was the inclusion of nudity and gore(unnecessary as Hitchcock proved in the first film). But I digress.
In dismissing the second and third film, he loses a major plot point. Norman's father was murdered at an early age by Mrs. Spool in her (Mrs. Spool's) perceived love triangle between Norman's mother, aunt, and father. Yet in Psycho 4, Norman says his father was stung to death by bees. That throws the entire basis of parts 2 and 3's plot in the crapper. But lets pretend Joe Stefano did that intentionally because he didnt like what they did for parts 2 and 3. Lets just say he wanted to take things back to part 1's ending.
Joe Stefano who wrote part 4, also wrote the original Psycho screenplay. If anyone should be aware of its continuity it should be him.
But he blew it. In the 4th film: Norman's mom met the guy she "threw Norman over" for after the motel was already built, and the highway had moved away, and Norman had been running the hotel for years. In the first film he stated "a few years ago, Mother met a man and he talked her into building this motel." Thats a big time goof. Especially since he wrote both screenplays. Also, Mother was established as "old" in the first three films. But since they wanted to use Olivia Hussey, he wrote in a one liner having Norman say she had "grown old" in his mind after she died. It was kind of mish mash.
I love the first one, the second was great, the third one was better than most sequels getting thrown around at the time....but I didnt like the fourth one much at all. For the above mentioned reasons.