Update: Adjustments have been made!  Overall, I am very happy with the adjustments.  All the new numbers will be bolded and italicized after the old numbers (only for those that were greatly overtracked/undertracked.)

I think most veteran users remember when adjustments came in a relatively timely fashion, especially when it was quite clear HW was under/overtracked significantly.  For the past few months, it seems like only small adjustments have been made, while some consoles are undertracked a few 100Ks, maybe even a few million.  Even in the face of recent official numbers, shipment numbers (Sony's being the latest) and Nintendo's sales charts, the numbers have largely remained unchanged.  Let me take you through the list of companies to show you what I mean.  I have bolded the ones that need correcting.

Nintendo

Wii U - 3.45M shipped as of March 2013 to VGC's 2.86M sold.  This puts 590K units on shelves.  This is probably close to reality.

3DS -31.09M shipped as of March 2013 to VGC's 30.12M sold.  This puts 970K units on shelves.  This is probably close to reality.

Wii - 99.84M shipped as of March 2013 to VGC's 99.27M sold.  This puts ~570K units on shelves.  This is probably close to reality.

DS - 153.87M shipped as of March 2013 to VGC's 153.9 sold.  VGC shows that Nintendo has sold ~30K units more than Nintendo has even shipped.  This means that the DS is most likely ~250K-300K overtracked.    Update: VGC nows shows 153.3M sold.  This puts ~600K units on shelves and is probably close to reality.

MS

360 - This is one of the more egregiously undertracked consoles.  77.2M shipped as of March 2013 to VGC's 75.01M sold.  This puts 2.19M units on shelves, which is highly unlikely.  If we say that 1.2M is a more realistic number (I'll be using this number for the PS3, as well), then the 360 is undertracked by ~1M units.    Update: VGC now shows 76.64M sold.  This puts 560K on shelves.  I feel this is slightly overtracked, now, by a few 100K.  I would imagine that in March, with sales slowing, but still coming off the holidays, MS would have at least ~800K-900K in the supply chain.  Still, much better than the ~1M undertracking.

Sony

PS3 - This is the most egregiously undertracked console (VGC no longer tracks PS2).  77.4M-77.7M* shipped as of March 2013 to VGC's 73.97M sold.  This leaves 3.43M-3.73M on shelves, which is not only highly unlikely, but darn near impossible.  Using the 1.2M number from before, the PS3 is undertracked by 2.23M-2.53M units.    Update: VGC now shows 76.34M sold.  This puts 1.06M-1.36M on shelves and is probably close to reality.

Vita - This one is harder to calculate, as its sales have been combined with the PSP from the start.  So, I'm not going to say it is undertracked or overtracked without real proof.  But to help calculate the PSP's numbers later, let's say it is spot on.  With it at 4.55M sold on VGC, this would mean that of the 7M the Vita and PSP shipped combined, the Vita would account for ~5M of it.

PS2 - 157.9M-158.2M* shipped as of March 2013 to VGC's 153.68M sold.  This has already been addressed by ioi.  In fact, VGC no longer contains PS2 HW data, except for in the Platform Totals.  So, while I don't need to go into detail about the numbers, I do feel the Platform Totals page needs to be updated, as well as be reserved for official shipment numbers.  This will cause the premature threads/articles/posts of "DS #1 Console" to stop completely.    Update: VGC now shows 157.68M in the Platform Totals.  This would put 220K-520K on shelves and is probably close to reality.  Hopefully, the other numbers will be updated, eventually.

PSP - Another console that is greatly undertracked.  Using the 2M left over from 7M combined I mentioned in the Vita section, then it is 78.3M shipped as of March 2013 to VGC's 76.19M sold.  This puts 2.11M on shelves.  Given the slow sales of the PSP, this is extremely unlikely.  The PSP is most likely undertracked by ~1.6M-1.8M.    Update: VGC now shows 78.73M sold.  VGC probably assumes the PSP shipped 3M of the 7M Vita+PSP shipped.  This is probably correct, as I made a mistake in my original Vita/PSP calculation.  I forgot the 1.8M the Vita originally shipped in FY2011.  So, if 3M is the real number, then this would put ~570K on shelves and is probably close to reality.

* - Estimate based on PS3 and PS2 shipping 16.5M combined for FY2012.  The PS3 was said to be down YOY, so the max it shipped was 13.8M (13.9M shipped in FY2011).  However, given that the PS2 only shipped 4.1M and was down 36% YOY in FY2011, I can't see the PS2 shipping more than 3M in FY2012.

So, what are your thoughts on the under/overtracking?  Do you think this will ever be corrected?  Or will the irregularities continue?

Don't forget undertracking on DS/Wii software.

DS is almost 200 million units undertracked.

Very true.  However, I would imagine it must be near impossible to calculate what titles are undertracked and where they are undertracked, so I'll cut them a lot more slack on that one.  Consoles, on the other hand, should be much more easily calculated.  There are only a handful of them compared to the hundreds of SW titles that need to be tracked.  They also ALWAYS get shipment numbers released for them.

honestly this is a great and much needed thread. great job man

This is a non issue for most items. Yes there is some like X360 UK sales are completely missing on some games. T hat is not undertracking but a complete error.

Here is the thing. 99% of every game on this site is probably under or overtracked by at least a small margin. Especially if you want to consider digital sales. The thing is they are estimates of sales from retailers and should be treated as such. As far shipping, that is what companies track. VGC tracks sold. If you want to follow sold then VGC will give you good estimates. If you want to follow shipments then follow the news when companies release info, if at all.

In the end don't expect 100% accuracy.  They are only estimates.  

I don't like this. VGC should contain PS2 HW data, not only in the Platforms total. I want to talk with "ioi"

Nice thread. Also pretty much all the software on current and older consoles are largely under tracked.
OT: But nobody is perfect box office mojo does a pretty horrible job with overseas numbers and a lot of their domestic numbers are off by a good chunk also.

Sen him messages.  Complaining on here won't settle anything. 

To expand upon the PSP numbers, it averaged 22.3k in the first quarter of the year in Europe according to Nintendo.  Meanwhile VGC has been putting it at less than a thousand weekly.

The problem isn't that estimates are inaccurate; it's that we've been given multiple sources recently which allow a greater degree of accuracy than estimates and nothing has been changed as a result of them.

Case in point (and reason I'm posting in this thread): PSP in Europe.

We have it at 37,118 January-April 2013.

Nintendo's chart has it at ~ 290k January-March 2013.

They don't have to adjust it to be exact.  They should've adjusted it to be in the right ballpark by now, though.