Update [Mon 7th Nov, 2022]: Since publication, we've updated the article with more info on how the artwork was found.
The Bugs Bunny Birthday Blowout was a platforming game for the Nintendo Entertainment System that the Japanese developer Kemco released back in 1990. But until recently, it was unknown who had designed the cover art. Now, thanks to the detective work of senior curator Sanford_US, and founder @Ibrahim_UK_ at OriginalVideoGameArt.com, we finally know that Larry Grossman was the person responsible.
The pair cracked the mystery after Sanford_US was able to distinguish a signature on a piece of promotional material. @Ibrahim_UK_ was then able to track down the artist and make a deal to acquire the artwork. They have since shared the discovery on the OriginalVideoGameArt website.
Along with sharing images of the original artwork which depicts Bugs and co standing atop a birthday cake, @Ibrahim_UK_ also gave visitors to the site the following description, which shows the condition it arrived in:
"The Bugs Bunny Birthday Blowout NES Box Art. The painting had approximately 1” at the bottom covered up with tape. The covered-up area does not appear in any published material. I carried out the conservation work and successfully removed the tape, and cleaned the leftover residue."
As noted in the comments beneath @Original_VG_Art's tweet, what's interesting about this is that the official box art seems to have removed the "Happy Birthday Bugs" message from the bottom of the piece. As @Original_VG_Art points out, though, this did appear in some marketing materials for the game.
@Ibrahim_UK_ is clearly no stranger to collecting video game art. Glancing at their profile on OfficialVideoGameArt.com, they also own Ken Macklin's original artwork for the Super Nintendo manual comic for Bubsy in Claws Encounters of the Furred Kind, as well as Julie Bell's piece for the cover of Super Valis IV on SNES.
Recently they told Time Extension that they started OfficialVideoGameArt "to raise awareness and appreciation for original video game artwork and the responsible artists."