Yes, but it wouldn’t be that far off. According to a link I posted earlier, Armstrong probably started 12 km from the top. At 7% gradient, that is 840 m, and if he did 30:45, that is about 1640 VAM or just 6.1 watts/kg. Nowhere remotely close to the 6.85 claimed by Ferrrari, or whatever it might come out with LA’s weight and 495 watts. If you assume 13 km, it comes out to about 6.6, which is close enough, but as far as I can tell the climb has traditionally not been timed from that far out.
What really bothers me is that people throw out these times without specifying exactly what the climb was. It makes no sense to list times of other elite riders of the past unless there is a well-established starting point that everyone uses. In fact, no one seems to know where anyone started, except the riders themselves.
Was Froome (with Porte) just making all this up? Maybe, given how reluctant they’ve been to release any power data, I did find it quite surprising that Froome would give both a time and a number. OTOH, given how sensitive Sky has been to critics, you’d think they wouldn’t make something up, taking the risk that they might be exposed as lying later.