One element of note, and something I was mistaking when doing my own calculations: Loncon 3 had over 10,718 members of all types, but only 8,723 of them were WSFS members (attending or supporting, with voting rights). Roughly 2,000 were single-day or other non-voting classes of member. Remember this when estimating what the total electorate was for the 2015 Hugo Award nominations: the union of the membership of the 2014/15/16 Worldcons as of January 31, 2015.
And here's another reminder: The Secret Masters of Fandom are not secret. Maybe we're a little slow sometimes (it's not like any of us are doing this stuff as our Day Jobbe), and often quite boring and tedious, but not secret. The only real secret of the SMOFS is that we're not particularly secretive.