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.
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.