Lol I think he showing surprise might indicate he didn't know, but did not he praise Vegeta's smartness in the Cell arc, saying he should already have figured how surpass the SS wall?
It's possible he knew, since he heard Vegeta say that he surpassed current Gohan before receiving the Majin charm. It could be that he was surprised at Vegeta becoming as strong as he is.
The Super Saiyan ascensions they were thinking of at the time were basic variants like Grade 2 and Grade 3, which Goku discarded in favor of naturalizing the form. SSJ2 is something different
I think Goku expected Vegeta to have attain SSJ2 within 7 years. As he did called Vegeta a genius and he should've figure out how to goes beyond SSJ in the ROSAT within a year.
I don't think Vegeta was at full power in SSJ. As it would explained why Goku was surprised at Vegeta transforming into SSJ2.
1. SSj Vegeta was at full power.
2. Goku could've calculate the SS2 boost and add to Vegeta's power which makes them even which he didn't because he doesn't know that Vegeta had SS2.
3. But Goku said he'll end the fight quickly as SS2 because he thought Vegeta can't beat him or touch him.
It is kind of retarded that Goku's shocked by Vegeta possessing the form when Vegeta said he was stronger than Gohan now, but then again, Vegeta himself was shocked at Goku flashing SSJ2 during Yakon, so it's just writing
Well both Goku and Gohan didn't know Vegeta had SS2 all along and were later shocked after they learned it. So according to Gohan, Vegeta and Goku are stronger than him excluding SS2.
Why would Vegeta deliberately exclude SSJ2 though? He clearly had the form since he could power up to it at the flip of a hat to counter Goku's SSJ2, and he later admits inferiority to Galu because of the latter's SSJ3 (which is far more draining and inefficient than SSJ2).