I was playing SMB3 yesterday and I noticed something very weird. The PAL version (which I currently own) of the game is pretty much the same as the NTSC version, but after beating World 7, I noticed a difference in Bowser's letter when compared to the NTSC version (which I had owned previously).
For some reason the European release has had the author of the letter changed from "King of the Koopa" to "Koopa Troopa". I don't understand this change because the European version was released after the North American one so they couldn't have made that mistake accidentally, unless they translated the name from the Japanese release again which wouldn't make much sense. Bowser has always been called "Kuppa" in Japan and from what I recall Koopa Troopas are called "Nokonoko".
JP letter: くっぱ (Kuppa)
US letter: King of the Koopa
EU letter: Koopa Troopa
The sentence "She's here in my castle, if you dare to try and rescue her." obviosly implies that the author is the owner of the castle. Therefore the conclusion is that one of Bowser's underlings had taken rule at the time of the localization and had ordered Bowser to guard the princess. On the other hand, while the castle may be in the author's possession, it doesn't necessarily mean that he has taken Bowser's place as king of the Koopas. Perhaps Bowser was just using the Koopa Troopa's castle temporarily. Making the Koopa Troopa go kidnap the princess was a jerk move though.
Anyways I am overthinking it and barely making sense anymore. What do you think?