Maybe Yoda knows of the Emperor and Anakin because Obi-wan told him of them when he became a spirit, or even actually showed him what happened in the past through his new Force Spirit powers. There’s also Yoda saying he’s been watching Luke, and something else is Luke mentioning Dagobah being familiar. Maybe Luke was brought to Dagobah when he was like two, and thanks to his strong connection to the Force Yoda was able to recognize his presence within it.

Yoda, along with other Jedi Masters, should be secluded from the Galaxy, with a Jedi Knight needing to further their training by seeking one out. Was Obi-Wab ever referenced as a Jedi Master in the OT? Maybe there could be a mediator between a Master and a Knight, an older Knight who helps apprentices start their journeys and eventually lead them to a master they themselves trained under. If Obi was a Master it still works fine, just that he was a younger Master who still wasn’t fully enlightened.