Question: Did contact outer plane work before Deities and Demigods was published?
Answer: Obviously yes. Otherwise it would be stupid to have a spell that did exactly nothing.
Question: Does the spell only contact deities statted in Deities and Demigods?
Answer: Obviously not. It says nothing of the sort.
Question: Does deities and demigods stat up all divine entities?
Answer: Obviously not.
Therefore, publishing stats for a subset of divine entities cannot inhibit the spell's function. Just like publishing stats for, say, Grezno, the half dragon celestial badger, cannot make summon monster impossible "because you can't summon monsters with templates other than celestial or fiendish, and now there's a celestial badger with the half-dragon template, which isn't celestial or fiendish, so you can't summon anything!".
By your logic, augury can't work either. Or the spell divination. Or any other method of learning the future.
By Rules As Written, you have an 88% chance of getting the correct answer. You CANNOT argue that, any more than you can argue that humans get +9 constitution. The percentage chance is EXACTLY what's written.
If you like, you can argue that the spell automatically adds knowledge to the entity's already vast store, and it's so irritating the deity only gives a one-word answer. But the fact that the extraplanar entity KNOWS the answer is inarguable.
As for a Rules As Intended argument, your interpretation makes three core spells completely nonfunctional. Given that they exist, this CANNOT be Rules As Intended.
Again, I'm fine with house rules, as long as you don't continue this ruse.