Sonic 1 Japanese Mega Drive - Yellow label

I just bought a few Japanese Mega Drive loose cartridges and there was Sonic 1 with a yellow label that I've never seen before. It seems underneath has the original Japanese label as well. Can anyone give me some info about it? Is it supposed to be in a console pack?

 

Yeah my first thought was "Bootleg" but then again who would bootleg one of the most commonly available (and oldest) Genesis games? Also part of me thinks that most HK consoles were PAL, so why would they use a Jap version of the cart?

 

Thanks for the replies!

Back side has the normal Japanese black label and it's intact, doesn't seem to have been opened.
I'll probably crack it open and see what's inside.

Actually this came with a bunch of documents from SEGA Japan and this fact excites me to solve the mystery. I'm thinking of something like a hack, but can't really find any playing differences.

 

looks like a replacement sticker has just been plonked over the original, you can see the original sticker through the top sticker.........can't imagine why

EDIT: sorry just seen you mentioned that in the first post, maybe it was a just a cart used to show the game in a shop or something so they wanted a more obvious cart

 

What do the documents contain? Probably more clues to the story about this cart in the documents than a picture of a cart label.

 

Sorry for the delay to reply, I still haven't opened the cartridge because I don't want to damage it. Here's a photo of the documents:



Mostly SPEC club newsletters, so previous owner should be a keen SEGA fan. I suppose the Sonic cartridge with yellow label probably was sent to members of the club back in the day to try the game before being released. This is the only conclusion I can imagine.