Just an observation but I well remember following this thread in amazement at the time but the thing that struck me about the very first post was the statement "Yes you do!!". I remember thinking that if only instead of that statement, the tower had been informed something along the lines that they had an extremely good view of the left wing of the Iberia and it currently had approx x cms of snow adhering to it and would he let Iberia know please, that it was possible, just possible, that the outcome of that incident might have been different.
Kind of like a CRM thing...
Or maybe I'm just kidding myself.
Anyway, and as per the ops manual, I am firmly in the completely clean wing camp, and if there is even a hint of doubt in my mind between condensation, or anything else, and frost, we do not move until MY hand has been on top of a wing, having had a good look at both of them.