In reply to Rob Parsons:
I'd wondered that as well, but have found a possible explanation. Have you clicked on the Le Dauphine article linked in Natalie's article? It contains an aerial view of the 707 crash site, and if I've interpreted the photo correctly the site was right on the summit ridge, immediately west of the summit of Mont Blanc, rather than somewhere on the Italian side as stated in the fr.wikipedia piece (maybe that's referring to the fighter remains, which seem to have been somewhere above the Sella bivvy hut). That would explain how some at least of the 707 wreckage was transported northwards in the glacier.
I descended that ridge in summer '67 on the way down to Val Veni after my first ascent of MB, but didn't notice any wreckage. Have I got the location wrong, was the wreckage already buried by snow after 1 1/2 years, or what?
Rob F