On the other end, Sega knows its leaderboards, who connects their games to consoles, and can most likely extrapolate sales numbers from that.
God only knows how much MS, Sony and Nintendo know about their customers. With >50% of all gamers being online for consoles, the big 3 have a litteral treasure trove when it comes to market data on their game sales.
For example, Sega probably has data for how many users owned Valkyria Chronicles and connected to the net via PSN. Through data such as that, Sega should be able to infer user sell through on the game. I would imagine that most developers can and do have the means to track users that way.
Back from the dead, I'm afraid.