blogiversary

 blogiversary  is a portmanteau of blog plus anniversary and refers to both the anniversary of when a blog was started and a post (usually a note, sometimes an article) that commemorates it.

IndieWeb Examples
Earliest first:

Kevin Marks
has been posting blogiversary posts since 2002.
 * 2002: http://epeus.blogspot.com/2002/11/blogiversary.html
 * 2006: https://epeus.blogspot.com/2006/11/my-blogs-fifth-birthday.html

Tantek
undefined used to post blogiversary posts, as recently as 2008:
 * 2008: 6th blogiversary

Manton
usually has a quick microblog post to mark the anniversary of his blog, and sometimes longer posts like these:
 * 2012: https://www.manton.org/2012/03/09/years-and-signals.html
 * 2011: https://www.manton.org/2011/03/09/wayback.html
 * 2007: https://www.manton.org/2007/03/10/weblog-th-year.html
 * 2006: https://www.manton.org/2006/03/09/mediocrity-is-the.html