Actually, I followed Kirby Super Deluxe through the press from prior to its Japanese release (as I've said before, this is the origin of my habit of calling it by that name - the name-change to "Kirby's Fun Pak" came only a couple of weeks before the PAL release, and we were never set to get the US "Kirby Super Star" name). I've known from the start when the correct date was.
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You certainly didn't need external contacts to know such things, as they were
very well-covered in the magazines of the time. This wasn't restricted to the unofficial ones who covered the import scene, either - even the official ones provided such information, which was a necessity to ensure customers that it really was coming to our region, since it proved that these things had already hit elsewhere.
That's neither here nor there, though - not knowing of something until later on still doesn't change when it actually debuted. For example, I didn't hear of Dragon Ball until 1996 - that doesn't change the fact that it debuted in 1984.