I don't know if she did or didn't post them, but
Tumbler can be set to post 300 posts in advance, so you can have 300 posts on your Tumblr after you die if you want, or 50 posts for 6 days after you die if you want. In addition, if anyone had her password or hacked her account (not as difficult as one might think), they could have posted those on a different day and changed the date. Since no one was thinking HE was missing until late on the 19th, it could happen.
http://www.tumblr.com/docs/en/advanced_post_options
And, if anyone has any computer saavy at all and had access to her account, they could change the time zone, which would change the time, then post, then change the time zone back. It might or might not show up in any Tumbler records, but we don't know if LE has looked at those or not.