I wouldn't use the word "transitionals".
Appreciate the extra shots.
In my opinion, the reason you won't find them in the books is not because they're rare but because they aren't the kind that people find very collectible.
It's pretty neat what you can see in marbles sometimes when you backlight them. However, keep in mind that if it takes a special light to see whatever was in the marble, then probably the maker of the marble didn't plan for it to be seen. There are some Mexican marbles which have dark surfaces and are covered with speckles. It's the speckles on the outside that are supposed to be seen. But sometimes, if you look really really hard, you can see cat's eye vanes inside. Weird things can happen inside the marbles. But if you have to work to see 'em, then they're curiosities, but probably not intentional.
That's the best answer I have for you.