Addressing unproven factual claims that underlie the laws of salting in prohibition and permission

In the laws of salting – there are many factual claims that form the basis of the laws – 1. Such as being anxious to spit out something that is not available to swallow. 2. The difference in swallowing blood by a piece of meat between blood in the eye and blood from organs or blood residues after salting. 3. Fish that spit out their entire intestines before the bird finishes spitting out its blood. Based on these assumptions – laws are determined regarding meat that is salted a second time, the need to wash before and after salting, and more. The disagreements among the Rishonim are also disagreements in the facts – for example – R.T. in salting several pieces of meat together – determines that in salting, blood spits out empty and therefore the blood is not swallowed, while other Rishonim say that the blood is indeed swallowed but spit out. What is the logic in determining a law based on unproven facts? What is more, it is also not clear on what basis each commentator decides when it is swallowed and when it is not.