Given that very few of the "open models" disclose their training data there's no reason at all to assume that the proprietary models have an advantage in terms of training on proprietary data.

As far as I can tell the reason OpenAI and Anthropic are ahead in code is that they've invested extremely heavily in figuring out the right reinforcement learning training mix needed to get great coding results.

Some of the Chinese open models are already showing signs of catching up.