As a recent historical corollary, one could ask how many men were in the Million Man March? So long as history names it such, the actual number won't really matter, as it's as much a symbol as anything. In this case, the numbers aren't quite so conclusive as the Long March, but the effects of a significant number remain.
"The Boston University team figured that there were 878,587 marchers. With an estimated error margin of 25%, the number of participants could have been as high as 1,098,234 or as low as 658,940."
Info found here:
http://observe.arc.nasa.gov/nasa/edu...llion_man.html