puzzled by fonts
I'm do some preliminary drafting, formatting, layouting etc in iBooks Author, and want to choose a good font or fonts for the book. I'm puzzled that in the drop-down Fonts menu in iBA, I don't see the four new fonts that Apple added to the iBooks app some months ago, namely Athelas, Charter, Iowan and Seravek. I'm equally puzzled that in iBooks, readers are offered only 7 fonts to choose from - the four just named, plus Georgia, Palatino and Times New Roman.
Why this discrepancy? Why are four (new) iBooks fonts not available when authoring a book in iBA? And why don't several of the fonts in iBA's own default templates feature in the list of font choices in iBook? In those iBA templates, the fonts which are used but which don't appear as options in iBooks are as follows: Baskerville, Helvetica, Bradley Hand ITC ITT and American Typewriter.
Any insight/enlightenment gratefully received.