Otakon 2000-2014 (taking a break; 1 year attendee, 2 years gofer/TCG, 13 years staff): 15
Anime Boston 2004-2015 (1 year attendee, 11 years staff): 12
Neko-Con 1999 (attendee): 1
NYAF 2009 (Dealer/Attendee): 1
Providence Anime Conference (there was only one and I staffed it) 2008: 1
ANEXT 2009 (Staff): 1
MangaNext 2008 (Staff): 1
I highly suggest waiting until Otakon officially announces their numbers to the internet before throwing out projected numbers. I don't see anything officially posted on the website, twitter, or Facebook page as of now. I know numbers were announced during Closing Ceremonies (I was not at this year's Otakon), so maybe once the official numbers are posted, there can be a better view of what the numbers actually are.