They were well-known by Einstein's time because by then they had been demonstrated many times. But someone had to have been the first to see and report the photoelectric effect.
What we need now is other physicists to test their own "Q thruster." If no one else detects a thrust, well, fine, chalk it up to weird error and move on. If other people do find a thrust, then we're into "we don't have a theory yet" territory.
Yes but they were very well known tabletop effects. What was lacking was the theory to explain them.