I think your maths are off anyhow? Since you do get 9 rolls (or less), but the amount of rolls you get don't change the percentage of succes. Even if you'd have 200 attempts to stop the bleeding, it would still be the same percentage for every single roll as the original roll had. The percentage to fail does not become better or worse if you've got more rolls in, even if we are inclined to think it does.
Unless I'm wrong and the NVN mechanics work differently and do increase your odds depending on the amount of times you failed before, but I doubt it... or else I haven't noticed it in-game whatsoever.
A 50/50 chance remains a 50/50 chance even if spread out over a hundred rolls. You have 50 percent chance to win every single roll and 50 percent chance to lose them all.
Not really. You can test this fairly easily yourself. Pick a six faced die, roll it 10 times, see how many times you never get 4, 5 or 6. Chances are you're getting bored before you finally roll it 10 times without getting 4, 5 or 6.
Thing is, you
only need to success a roll once during those 9 rolls you have. The mathematical proof (which I can't really remember to letter right now) has to do with number sets, but basically, there's a fraction of rolls that are in certain range. You have to land on that certain fraction, and land on another fraction again (the same fraction), and another fraction of that; As such, the likelihood can be calculated as fraction * fraction * fraction.. For amount of rolls you have.
Another way of thinking this is geometrically. Draw a simple circle, split it so that the split area matches the likelihood of rolling to that area. Next, split that area again to same relative size, and again and again.. The area will get a lot smaller and smaller on each successful slice.
While for any specific roll the chance to be anywhere from 1 to 100 is exactly same, for successful rolls the chance to be same diminishes.
Still not sure how con influences this, but while I have a relatively high con on most chars, I don't seem to notice a percentage much different than something between 90 or 88 percent?
Well, due to the above, having even small increase in the percentage kind of "stacks". For example, if your hitpoints were at -4, you'd have 50% chance to survive if your constitution is 10. With 14, your chance is 56%.