IIRC Gyromite is the most common of the carts with adapters inside. Not the only one, not by far, but the one most people have found them in.

None have been found in any of my 5 screw carts, but most of mine are from late 86 or later, I have no 85 stuff (and no Gyromite at all), which would be the likeliest carts to look for if you had a way to narrow it down to that.