I don’t regard my own answers as canon when they haven’t been recorded in the text itself, but Opinion of God is that the Interdict of Merlin applies to magical secrets that can directly or indirectly lead to wide-scale catastrophes if revealed. (It’s possible that Harry’s Brown Note for the Patronus Charm would fall into this category, even though it’s not a secret that causes a nuclear-scale explosion as such.) Harry Potter and the Methods of Rationality includes instances of people learning relatively strong magic from books (e.g., Tom Riddle and the original horcrux spell), not to mention that Hermione is explicitly shown in-scene to have learned sixteen spells just from reading books. It’s implied however that the art necessary to create e.g. the Deathly Hallows, or to raise Hogwarts, was unrecordable and therefore lost.
Eliezer replied on stack exchange: