If you're talking about sales over a particular fiscal period (where you neither have an unexpected shortage of units nor a building surplus) your sold to retailer numbers should be roughly equal to your sold to consumer numbers.
Basically, a retailer will want to carry a certain number of units depending on how popular a system is and this number will (probably) not change drastically unless the popularity of a system changes drastically; therefore they should be replacing a sold to customer unit with a unit they bought from Sony.
Sony, Microsoft and Nintendo don't actually track sales of software/hardware themselves but they do estimate sold to consumer numbers using an equation that would (roughly) work out to be:
Sold To Retailers - Retailer Inventory = Sold To Customers
The equation would be more complicated than that because they would have to calculate retailer inventory, but the core idea of the equation would remain intact.
