The way the database is currently constructed, the only reason why you would add it as an entry (and into your collection) would be if you were to have purchased it just to have it. This concept is not outside the realm of possibility however.
Since you can't assign an item to another item, it doesn't make sense to have it there. So you probably should just edit the Note on your NES entry and put in there that it contains Blinking Light Win.
I still feel that it will eventually show up somewhere. If it were to be classified for the current db sections I would say NES Accessory.