NeverarGreat said:

Has everyone forgotten that Yoda clearly stated in ROTJ that Luke was the last of the Jedi? I figured that if he was able to sense Luke on Tatooine and watch him, he would easily have been able to locate any other Jedi who managed to survive the purge. If another Jedi did survive, that makes two Jedi who lied to Luke's face.

Yoda did not sense Luke on Tatooine. He sent Luke on Tatooine.

And not to forget that he never felt that a Sith Lord was running the republic under his nose. That makes Yoda's power to "scan the galaxy" from Dagobah in search for other Jedi more than doubtful. (all this if you acknowledge the prequels existence, of course!)