A lot of the glob ones don't tell you anything when you decap them either unfortunately, especially once we're into later 80s / 90s tech. I think 'mask ROM with visible bits' is the least common of the techs.
I fear a lot of these are going to require much more advanced techniques (microprobing / microbonding to read out ROM arrays directly etc.)
Yeah that's true, the Gakken games seem to fall under this category unfortunately, Gakken Soccer was one of my favorite LCD games when I was a kid, but after decapping it shows no visible bits.
