@highergeometer There's a theorem in probability theory that says that if you have the probability P(H|E1) of some hypothesis H given evidence E1, and the probability P(H|E2) of the same hypothesis given some other evidence E2, then the probability of the hypothesis given the conjunction ("and") of the pieces of evidence can be anything between 0 and 1 included:
P(H | E1 ∧ E2) ∈ [0, 1]
In other words, more details must be given.
See T. Hailperin: "Probability logic and combining evidence" <https://doi.org/10.1080/01445340600616289>.
In the present case it depends on the relationship between the two agents. If you give me your rolls and I trust them, I might add them to mine and update my probability for the next. Or I might not fully trust you, and therefore use them only conditional on some sentence T expressing that what you say is true; the result is that your rolls would be weighed less than mine. It also depends on my prior over the possible long-run frequency distributions. For instance if it isn't exactly exchangeable, I might increase the probability of the hypothesis of a "changepoint" or a different rolling technique (the way of rolling or tossing can give much more bias than the distribution of weight in a die or coin) between your rolls and mine; see <https://doi.org/10.48550/arXiv.0710.3742>. The possibilities are endless.
It seems unlikely to me that a product formula like the one you give would come up in some situation, but right now I can't exclude it.