What happens if a mage writes a Casting Tablet with a particular Spell Mastery option (eg the mage has Flawless Magic)
Can another magus without any Spell Mastery abilities use this Casting Tablet?
And potentially the other way around. Can a mage with Flawless Magic use a Casting Tablet written by a mage without Spell Mastery?
Don't have the book in front of me. Can Casting Tablets be successfully copied by anyone apart from their author?
I don't see in Covenants that Magi can write Casting Tablets that include Spell Mastery abilities as part of the casting.
To write a new casting tablet, the magus simply has to have mastered the spell that she's going to write the tablet for (any mastery level or mastery ability is sufficient) , but any magus can attempt to use it, with varying chances for success. Magi with no Mastered spells cannot author casting tablets (but can copy existing casting tablets).
Magi must have a spell mastered to author a casting tablet for it, Flawless Magic is not a requirement in any way, except that a magus with it has it waaay easier, and could potentially create casting tablets for all his formulaic spells without spending even 1 xp on Mastery abilities, if he so desired. Most magi can master spells, some with more difficulty than others, so there's almost always the possibility of authoring such a book.
Yes, from Covenants "magi can copy tablets written by others."