I don't agree with the black and white assumption that there is either proof or there is nothing. Einstein presented scientific papers in 1905, the miracle year, where he proved his theory of special relativity. It threw the scientific world on its ear. His theory only worked when objects moved at a constant speed. Einstein knew his theory applied to everything in the universe but his calculations fell short when you allowed for acceleration.
Einstein proposed his theory of general relativity in 1915 and it took an eclipse in 1919 to prove it. So, from 1905 to 1919 there was no "proof" of general relativity so everything from 1905 to 1919 was "conjecture". In between those years was his theory which needed to be proved and this theory, I would submit, was far more than mere conjecture.
I will also submit that until such time as a sasquatch is proven to exist, there is a lot more than mere conjecture. Much more.