But it also applies to the model. If you label data taking into account the context (which subreddit this was posted), your model also must take this into accou

But it also applies to the model. If you label data taking into account the context (which subreddit this was posted), your model also must take this into account, or it will be wrong as well. If the same sentence can be labeled two different ways depending on the source, then, the model must also know the source or it won't know what to do. But then you didn't create a general language model, you created a reddit language model.