User blog comment:BertH/Introducing WAM/@comment-167456-20130505064925/@comment-452-20130506124218

Good question - it appears the first column is just the row number.

So it appears there are several top-5000 ranked wikis we cannot see in the list.

For 2013-05-06, if you view a single Vertical, and go to the last page: Total missing from individual verticals: 751. So there are 24 Ranked missing wikis which don't fall into the vertical categories.
 * All - Row #4224, Rank: 4999-4224 (775 missing)
 * Gaming - Row #1803, Vrank: 1803
 * Entertainment - Row #2349, Vrank: (115 missing)
 * Lifestyle - Row #72, Vrank: 708 (636 missing)

Hopefully Bert can shed some light on this.