This data should be used in the absence any other way to verify sales. The other markets sales cannot be made any less reliable through this process. In fact I welcome the prospect of actually getting something approaching full sales data for dozens of games which VGC cannot seem to be able to track in the other regions. Despite the fact that you know they are selling.
I think however your a little aggressive with your multiplier. I find it hard to envisage a 360 title in Europe tracking near the 360 titles sales in North America. Even Grand Theft Auto IV has tracked at about forty percent of North America. What I am meaning is to say is your estimates are too positive. Anything beyond fifty percent of North American sales should be discounted immediately.
A better multiplier would be have a percent. Use the MGC data multiply it by half a percent and then add the result to the MGC data. That should give you better data that is both conservative, and probably closer to reality. For example this would have Blue Dragon being just over 90,000. Which is closer to forty percent of North America.
I think you should use Grand Theft Auto as your measuring stick. That should define your limit for estimates.







