There has been some discussion on how alogs are ordered on the web page. Here is what I learned this afternoon after speaking with Ryan.

Each page displays 20 entries. These can be new entries made recently with no comments or new entries with recent comments, in which case they are listed in chronological order of the initial post.

If any of today's entries are comments to an old post (one which would normally not be displayed in the page) then the initial post is shown in today's page, along with every comment it has garnered including today's comment(s). These "promoted" entries are shown at the bottom of the page in chronological order of the initial posting.

For example, at the bottom of today's (Friday 05 June 2015) first page there are two old posts which were commented on recently, they are in the order: 

evan.hall@LIGO.ORG - posted 21:21, Thursday 04 June 2015 - last comment - 12:47, Friday 05 June 2015(18878)

kiwamu.izumi@LIGO.ORG - posted 11:16, Friday 29 May 2015 - last comment - 14:45, Friday 05 June 2015(18693)

Note the order of the initial post, not the order of the last comment.

Therefore the alog entry numbers can be out of sequence. Also some numbers may not appear at all if they were assigned to a draft entry which was subsquently abandoned.