There are plenty of 3P and R2 series robots running around. There’s no reason to believe he thought he knew them.
Further, there’s a comic where he sees C-3PO’s blasted body and has a flashback. So even though they didn’t share the screen, Vader did share a moment.
My actual biggest issue is that Vader stood in front of Leia and didn’t seem to have any idea that she could use the force or that she was his daughter.
There are plenty of 3P and R2 series robots running around. There’s no reason to believe he thought he knew them.
Further, there’s a comic where he sees C-3PO’s blasted body and has a flashback. So even though they didn’t share the screen, Vader did share a moment.
My actual biggest issue is that Vader stood in front of Leia and didn’t seem to have any idea that she could use the force or that she was his daughter.