In the instruction insert within the Gremlins board game, there is a short narrative that exposes further plot elements in the Gremlins universe. Whilst the author of the narrative isn't referenced, the production company certainly is, and thus I would imagine that there had to be some degree of collaboration with screenwriter Chris Columbus. Is there any references or indications the aforementioned narrative is canonical.
Until today I didn't even know there was a Gremlins board game. That said, the Star Trek novels prove that something doesn't have to be canon even if it's released by the same production company.