No

GPT models were internally available 6-12 months before they've seen public beta, of course OpenAI has more capable internal models.

There's no reason to believe this. The training time and cost is so substantial that they are almost certainly building their next release, but it isn't sitting there rotting.

Much of that training time is RLHF, the absence of which does not make the model less capable of carrying out useful tasks (indeed, in case of GPT-4, it actually made the model slightly less capable).

OpenAI themselves have said they hat GPT-4 internally before they ever released the first version of ChatGPT.