Does that number include life members?
I made an error while posting pulling info from a spreadsheet I created (I subbed the number of domestic members voting for international members). Domestic membership is 15601, international is 1652, and at the top of the list on the certification document is a blank location reflecting 870 members? That's a membership of 18,123 as of 1/17/18.
I'd suspect that lifetime members would be reflected within those numbers, and included in the total for their respective countries.
The document has a link on the front page of the KCBS site. A member account is required to view it.