Questioning the Validity of One Stadard Value Chart
Harry Green has an interesting take on this on a separate thread.
Essentially, that - because the pool of draft prospects varies (a) in depth, (b) in overall talent, (c) in talent at the top of the draft board and (d) by position, the value of a high pick in relationship to the value of a bundle of later picks will vary from year to year.
Therefore, the value number assigned each slot should be adjusted from year to year.
Thus the trade of Spot #1 for, say Spots #7, #10 and #40 might be dead-on (at 3000 pts) in Year A; but in Year B, the value of Spot #1 might be worth more and the value of spots #7, #10 and #40 might be worth more, the same or less - so that the trade value would no longer be dead-on.
My guess is that each team has its own variation of the Value Chart, and that some might adjust the numbers from year to year. If two potential trading partners have arrived at basically the same conclusion about the numbers, they'll make a trade. If they don't agree, the deal probably won't get done.