In normal models it's been weird for years, but at least in the performance models they should stick to the numbers. But even the "63" models were wrong, the engine is 6.2. Sorry if somebody is in marketing, but sometimes I just hate the stuff they make up. "Hey, let's use 6.3 because it has historical connection, nobody cares about 0.1l!" and then later "Hey, it might be 5.5 but we had 6.2, which was called 63, before, so the new model, even with twin turbos, can't sound worse than before! It has to be 63!".
If I were an engineer working with these geniuses, I'd really need my 500+ bhp to cool me down. And don't let me start with the BMW Z4 sDrive35iS stuff, that naming really doesn't belong to awesome thread, quite the opposite.