nordlead on 21 March 2008
Manufacturer numbers are only released on occasion, typically just with their financial reports, which are once a quarter. These numbers don't show up till after NPD and VGC has reported their estimates. So corrections can only be made at a later date.
NPD does not release their corrections to the public, only to their paying customers. So we can't see if NPD corrected using hardware shipments, but I am sure they do. You can see when VGC gets updated, since the historical weekly sales are always accessible.
