OoP : How many death eaters? bit of a mystery (spoiler)

[sueeeyqbong]

No: HPFGUIDX 64526

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Hi everyone. Something else I've just thought of, after reading the 
scene where Moody shows Harry the photo of the original Order of the 
Phoenix...in the photo, Moody names 20 or 21 members of the original 
order. Later on, during the boggart and Molly scene, Lupin comments 
that the order is much better off now than last tme, because back 
then the death eaters outnumbered the order 20 to 1. That means that 
back then there were at least (roughly) 400 death eaters. How come, 
then, in GoF when Voldemort summons the death eaters to him at the 
graveyard, there aren't anywhere near that many death eaters around 
him...I haven't my GoF copy near me, but I'd guess less than 20 
death eaters returned to him. Add to that a handful of death eaters 
in Azkaban (10 at most?) and that only makes around 30 death eaters. 
What do you all think happened to the rest of the death eaters? If 
they all died,  that would imply a battle of some sort to me, and we 
certainly haven't heard of anything ike that up to now.   Any ideas, 
anyone?