Ancestry doesn't perform a "live search" of Find A Grave. They (Ancestry) created an independent index which is updated periodically. So, memorials created after the index will not appear on the index until the next update. From the citation:
Ancestry.com. Web: Indiana, Find A Grave Index, 1800-2012 [database on-line]. Provo, UT, USA: Ancestry.com Operations, Inc., 2012.
Original data: Find A Grave. Find A Grave. http://www.findagrave.com/cgi-bin/fg.cgi
: accessed 25 January 2013.
So, I would guess the last update was late 2012 (given "1800-2012" dates) and the memorials were created after that.