I agree with you about seeing how the draft plays out and go from there, but the board being set has a lot to do with trades. You create a draft board for value of the prospects. If a teams value of players drop off after their 10th rated player, their not trading down past 10 (most likely). Until you have a final board no team knows how far they will want to trade down. That's why trades are not usually made until boards are pretty much set. Yes they have preliminary talks bout trades months in advanced, but nothing usually gets done early on because no values are set on the prospects.(Colts had a deal they couldn't refuse with the jets, to only move down 3 spots). Having ur final board set has a lot to do with trading picks before/during the draft. A team could feel good moving down 10 spots bc they have a big clump of players rated equal, so they would make a trade knowing they will get someone they like and pickup draft pick assets.