Sorry let me clarify my last statement. I have not trained all the recipes from the vendor, I have however stopped benefiting from Northrend Inscription Research (as I only get random scroll and not a discovery). Once this happened I started buying Books of Glyph Mastery and training from them, until last week when I used a Book of Glyph Mastery only to get an error message saying I could not benefit from that item. Thankfully, it did not consume the Book.
Lessons I learned:
1. You do not need to train all the vendor recipes. You won't learn any of these by Research or through Books.
2. You cannot learn all the glyphs through Research alone. Since (I believe) I had learned all the Research glyphs before I started on the Books of Glyph Mastery, I can't say whether doing both at the same time is counterproductive, i.e. whether they randomly choose from the same or different "lists" of glyphs when you do research/use a book.