you're again assuming that the warlock knows these things are coming from another being, they could be entirely convinced they're just figuring out and developing these powers themselves or that their familiar came to them of it's own accord, the blade was sold by a shopkeep who didn't know what they had on their hands, the tome was found in a pile of loot or at the dusty back shelves of a library,
it's so easy for a patron to put these things in their warlock's path for them to 'find' without them knowing a thing, and the reason is the same as before, it's an investment, they give a little, a crumb of their power, and when they get it back that spark might've turning into a powerful flame.