You guys have a source for that? As I remember it, the trade was filed with the leage the night before but Betman requested it not be announced until the start of the draft.
Pretty irrelevant distinction regardless. Benning had some ideas on who would be available at 24 and felt he'd get a good prospect. He was right. Gillis also felt he'd get a good prospect at 9. Again, correct. And during the Ballard traee, Gillis didn't think they'd get a good prospect with that pick, so they dealt it. Yay, 3 for 3!
As for the overall discussion, I think it's more accurate to say it depends on the pick and the year. Obviously you trade a 6th for Weber and that 6th turns out to be Datsyuk it doesn't change that deal. But 1st rounders are a bit different. When all 3 deals above were consumated the GMs should have had some idea about who would be available. When you are talking about 1sts with the draft imminent (compared to say we dealt Vrbata tomorrow for a 1st) I expect a GM to have an idea of who he's getting, even if "one of these guys".
Using the two Gillis trades as examples, Gillis deserved credit for recognizing a deep draft giving extra value to #9, and he deserves credit for recognizing a shallow draft lowered the value of 14 or whatever it was that year.
Likewise Benjing deserves credit for getting a pick with which he'd be able to get a good prospect, even if it wasn't necessarily MCcann he was betting on getting.
If you are talking later round picks, I agree that the value at the time doesn't change depending on how the picks turn out. But when you acquire a 1st with the draft order determined, you should have some idea of who is going to be available, and thus who you pick ends up factoring into whether you got a good deal.