I think what MeBe is saying is if you watch the OT and then when you get to the ROTS in the prequels the movie says there is another Jedi. Because Yoda's death is implied rather than shown, and we know Yoda is alive and well on Dagobah in TESB, than when we hear that there is another Jedi around by the end of ROTS, we don't think Yoda, we wonder who this other Jedi is. It is only hinted that Yoda died at the end of the ROTS, and since we know he is okay, we don't necessarily connect the two.

That's what I got from the OT > PT surprise. If that's not it, then maybe MeBe will explain it for us.