This has been explained to you so I don't know why you're having such trouble understanding. Here is the article I posted the last time:
No such thing as scientific proof.
Common misconceptions about science I: “Scientific proof”
One of the most common misconceptions concerns the so-called “scientific proofs.” Contrary to popular belief, there is no such thing as a scientific proof.
Proofs exist only in mathematics and logic, not in science. Mathematics and logic are both closed, self-contained systems of propositions, whereas science is empirical and deals with nature as it exists. The primary criterion and standard of evaluation of scientific theory is evidence, not proof. All else equal (such as internal logical consistency and parsimony), scientists prefer theories for which there is more and better evidence to theories for which there is less and worse evidence. Proofs are not the currency of science.
So, let's take the blood type example you're tenaciously holding on to. That there are four blood types is an
observation. It is not a prediction or a hypothesis. That said, where the "proof" aspect comes in is that it is not proven that there actually are four blood types or that there are only four blood types because, and I'm bolding for emphasis,
future observations might show that to be incorrect. Again, the lack of "proof" in science has ZERO to do with what we know now and everything to do with what we
might learn in the future.