Oliver mentioned finding a message from his father "a couple of year's ago" in S1. I believe that's what AndreTheGiant is referring to when he says "confirmed the list".

I thought the list was confirmed because of that scene in BBB when Felicity brings him the (second) notebook / list, which she obtained from Walter. He knew that the mere presence of the second book meant something significant, particularly since Felicity hinted that Walter got it from Moira.