Well that's interesting. I think they just have secured the supply for your car and for March delivery they need the car ready around January so it's not that long away. But I'd recommend calling Tesla and asking what exactly does it mean in your case.
I have a feeling that they are building cars in batches for European/US markets respectively, and then it is a question if my car would be delivered at the agreed time if they don't make it in this batch. This batch should be for delivery in January/February. I am guessing that my car will be produced at the end of this EU batch and shipped over late.