There are words/tokens that are heavily correlated to the prompt (a yes or a no, for example), and then there are others that are going to be less so (adjectives with a lot of synonyms for example).
Given a text, you can identify what the "load bearing" and auxiliary words/chunks are. Then, looking only at the auxiliary words/chunks, you should, in principle, be able to determine what other wordings could have gone there instead. From this, you can, very roughly, recreate the token probability distribution that was in effect when those tokens were generated. With the probability distribution in hand for enough chunks of text, you can start inferring properties about the RNG process that was used to sample from those distributions.
But then, this notion of "load bearing" vs "auxiliary" can be expressed directly in the probability distributions. A load bearing token just has a very high probability, and thus any RNG bias that may have been in effect will likely be swallowed in the distribution. So the parts of the text that are highly dependant on the prompt will naturally not be contributing much information about he RNG in the first place.