I don't think it really matters whether Seb Coes' weekly mileage was 10 miles or 200; he had to work hard to get to where he did either way.
The people who want to believe that Coe did low mileage seem to be looking for an excuse to run less. What they don't realize is that, to train as Coe supposedly did, they would have to work just as hard, if not harder, as Joe Elite middle-distance runner running more volume than Coe, except through quality-oriented pace sessions rather than mainly aerobic volume.
As for the people who want to believe that Coe did more mileage than he states,
it seems as though a lot of people want to believe that he trained one way or another to justify their own beliefs with regards to training. I don't think anyone is ever %100 certain that what they're doing is the absolute optimum. What you can do is continually educate yourself about training, about your body, how it responds to stimuli, and just in general always try to be progressive in your training; tweak it and always look for ways to make yourself a little faster, whether it be through adding miles, little drills, whatever... that's how Reid Coolsaet got from 15:51 to 13:21 in 4 (I think) years...
Also, whether or not Coe did high or low mileage... the whole "low mileage" thing probably psyched out his competitors pretty good!
Except Ovett... ah, good ol' 100mpw-in-base-period Ovett...