About that "official name". Don't be surprised if Model Y actually ends up with a different designation.
From Q2 2017 Earnings call transcript:
Elon Musk: "No, that's one of the things that we would include. We would aim to switch out the wiring models for (inaudible) the wiring models for a redundant flex circuit that's more in the order of 100 meters or so. But -- and then we'd -- obviously, we'd aim to do that both for the Y, if it's called the Y, and the 3 as well."