In the marvel comics Vader and Luke meet for like a minute and Vader sees the lightsaber, knows it’s his, and then sends some bounty hunters to figure out who the kid is. So in the new canon Vader knows who Luke is.

That being said it works with both versions of Empire but more so with the OUT.

In the OUT Vader just knows and everything moves on as normal.

In the SE versions we would just have to assume that Vader found out, kept it from Palpatine, and then just played dumb when Palps told him about Luke.