spells that are really that complex require multiple individual spells to combine and utilize the book binding process to bind the script together while still maintaining the integrity of the individual spells.
Ok, so I guess then my question is more - is there a gradient in the complexity of tomes? I understand they're for spells too complex or interconnected for a scroll to be practical or the preferred delivery method, but is there such a thing as a spell that would be too complex for a single Scroll but wouldn't be befitting of a capital-T Tome like the 2 you described above?
OR would such a too-complex-for-1-Scroll Spell that's also too-simple-for-a-Tome just be written across 2+ Scrolls instead and there is some mechanism by which you can link them independently of having to put them in a Tome?