OK, that makes sense, but by that rule games like Gunhed shouldn't be numbered either, right?
And what about Bonk (PC Genjin)? Wasn't Bonk done by RED and just published by Hudson Soft?
And R-Type? You know, with R-Type it's funny. Hudson is credited on the dual-HuCard release, but there is no mention of Hudson having anything to do with the CD version. They aren't even listed as a publisher for the CD version. Either way, Irem holds the license, so those shouldn't be numbered either.
Oh, well, it'll probably never make sense anyway.