I think their original goal was 100, but perhaps they were restricted by the current macro book size... or perhaps theres pages, I mean they show 20, and there very well could be 5 pages of 20 you can cycle through (though, honestly, I guess i could have overlooked them specifically saying 20)

That said, I could probably make due with 20 if I just used my THF and SMN... maybe RDM if I still make some swaps in the macro books... but yah, It'd be real hard.