The quarterly numbers are the biggest help for adjustments as we generally know how the usual gap between shipped vs sold. Though, right now that gap is far smaller than usual due to the shortages. Even Switch stock is more limited than what is typical.
One way I use historical data is looking at how much above or below PS5 and Xbox Series X|S sales are compared to PS4 and Xbox One. And for Switch how well sales have been compared to last year, 2 years ago, etc. Of course I also use all available data.
Not to mention Sony mentioning their own estimates of sell-through when there is a milestone or how close it is compared to PS4. I would say that for any given month VGC could be even 25% off (not normal), but when looking for LTD it would be less than 5% off.
duduspace11 "Well, since we are estimating costs, Pokemon Red/Blue did cost Nintendo about $50m to make back in 1996"
Mr Puggsly: "Hehe, I said good profit. You said big profit. Frankly, not losing money is what I meant by good. Don't get hung up on semantics"
Azzanation: "PS5 wouldn't sold out at launch without scalpers."