Glad it's not just me that can't get that bit working... it was driving me mad (how appropriate!)
Reading the Realms of Cthulhu book a bit more, I think the sanity loss will need to just be a manual addition when they read the book as the sanity can be cured with therapy; which you can't do if it's bootstrapped to the Hindrance. The general HL error checking does warn that the Knowledge skill hasn't been completed, so I've put a note in the Hindrance text to note that they will need to add Mythos manually until a workaround is found.
The other issue I am having seems to be the same one that Zalor was having in his
+1 Skill die or start with d4 thread. Did you ever get a response on that, other than to have two different hindrances? I've created two hindrances for use after you get rid of the book to either add, or increase Knowledge (Mythos), but that doesn't really help with the book itself, unless I have two copies of the book...
I'm currently trying to work out if there is a better way of handling the book as there will be others in the future. Current thinking (which may not be the best on 2 hours sleep) is that the sanity and knowledge effects should be removed from the book altogether and just handled as the hindrances/injuries that come into play when you translate the book. Only the spells should remain bootstrapped to the books.
With that all now up and running with workarounds... back to typing in equipment and spells :/