Hi there,
I think "C65" is a pretty interesting name. It's very non-technical (C64, C128, C16 all have their names because of their RAM sizes for example), it's more like a nickname given by users or something like that. As far as I know, the previous code name was "C64DX", which would suggest "C64 Deluxe". Later it was called C65 in media and so on, but there has never been a type label / name plate on any of the models (as far as I know).
Of course the name makes sense, it's "one better", just like C++ is "C plus one". It's also funny in this regard. But that's why it sounds so informal and untypical. It could have been namend C64plus, or C64+, or C64next, or whatever. But C65 is pretty... strange somehow. Not that I dislike it, it's actually cool in a way. But it's very unusual in another.
So how certain are we that the official name would have really been "C65"?
Have there been official documents / advertisements or whatever, that really suggest that the final name of the unit would have been C65?