According to IGN and NPD, every Capcom-Wii game is overtracked

[Erik Aston]

I think VGC is probably an acceptable 5-15% over for a lot of titles in the first few weeks, but then 50-500% off in a lot of the legs tracking.

Remember that a lot of these games have already had corrections in the past, because Capcom shipment data is more common than for most other companies. So VGC may have already corrected down to Capcom numbers for 50% or 75% of the total sales, and then still subsequently overtracked by 15 or 30% of the total.

This is unavoidable as long as VGC keeps putting numbers out there for gazillions of games every week. If VGC covers 5% of the market, for a title which they estimate sold 5K copies, they only directly tracked 250. When a title is selling that little, maybe most retaillers have dropped it. Maybe a retailler VGC covers is the only one carrying it. Or maybe the retaillers VGC covers are some of the only to have stopped carrying it. You can only undertrack in a given week by the amount of weekly sales though, while if VGC covers 5% of the market and covers all of the sales of a particular game, they could overtrack by 20 times the actual sales in a given week.

Even the biggest sources only put out numbers for the top group of games. Rarely will you see sales for more than the top 40 SKUs in a country in a week, and that's from people with far more market coverage. Meanwhile VGC lists not just the top 200, but hundreds and hundreds beyond. I think VGC has done a poor job of developing their legs tracking because those numbers rarely get attention compared to first week data, and they can always fall back on "percent of total" instead of "percent of total since last correction."