Something Beth might've overlooked in the dialogue.
In Season Unending, after the negotiation is over and all attention is drawn to how to lure a dragon to Dragonsreach, Esbern offers the solution, saying this:
"I anticipated the problem. While you were arranging this meeting, I was busy in the library of Sky Haven Temple. An unguessed trove of lost lore… but the important thing is that the Blades recorded many of the names of dragons they slew."
The thing is, he still says that even if you decided to let Elenwen stay at the beginning.
Of course, there are no consequences because this is entirely optional and the devs probably didn't give it much thought anyhow.
Still, it's odd that it's possible to have him openly mention the Blades hideout in front of the Thalmor first emissary. A slight dialogue change for that scenario would've made more sense.