Hello, oh you have helped more than you realise indeed!
As you have the red disc, and i'm guessing that's the colour the USA editions were pressed, thank you for letting me know
Anyways the slipcases, there there produced for at least the European & USA first pressings of the album in 2001... they made them with the slipcase until they began distributing them without the slipcase in about 2004/5ish in just the jewelcase as standard.
I don't know why they stopped making them with the slipcase, I guess ultimately for Sony it saved money then they went out the charts and became back catalogue albums.
This was also around the time that they began releasing the 'x2' doubles of the two remasters in a slipcase 'as pictured below'... it's just the photos of the cover with the tracklists on the back, the CD's are no different from the remasters that you and I have.
I guess when you get them second hand they can be with or without the slipcases of course, depending on if the original owner got it with or without. Also there is the possibility of the first owner taking off the slipcase and mispalcing it sadly.
I still sometimes see the odd slipcase edition in shops from time to time.
I know ultimately the slipcases don't matter, it's another finer detail... but they're to have I guess.
I hope that sort of helped you=)
Lv Francis x