The original plan was all those four Special Editions to include bonus audio material.
So, the ‘Dangerous - Special Edition’ was about to include bonus audio material too, so the ‘Special Edition’ title was also printed on that release.
But, the bonus audio material for the ‘Dangerous - Special Edition’ needed an additional second disc due to the fact that the original ‘Dangerous’ CD already reached its maximum audio capacity (around 74 minutes).
In the end, the record company decided not to include a second bonus disc for that release because a double CD would not be commercially successful.
“…When the album ['Dangerous'] came out, I think it was 74 minutes which was maximum capacity for a CD. It wasn’t physically possible to include bonuses without a second CD and I believe it was a commercial decision taken by the record company not to go down the route of a second disc. But we had reviewed material in case we were given the go ahead…” (Matt Forger)
But the ‘Special Edition’ title remained for the ‘Dangerous’ release not only because it was already printed on that release but also because all those four releases had to have uniformity on their titles.
Of course, the record company tried to justify that ‘Special Edition’ title on the ‘Dangerous’ release by some other features (such as, remastering, new booklet/packaging with new photos).