Firstly, go to post #613900 and read the comments.
Basically, for that post (as well as post #613893), there seems to be a bit of an issue: If you read the comments, you'll see that the artists 'sylph' and lasterk both seem to share content.
The sylph/olin account seems to have posted the Hitagi pillow image first on Oct 7 2009 in their blog while lasterk posted a higher quality uncropped version later.
The sylph/olin account also seems to have posted the Horo image first on July 14 2009 while lasterk posted a higher quality uncropped version later.
The lasterk account seems to have posted the Mio image first on Jan 2 2010 in their blog.
Given that, I say file them both under lasterk for now since sylph/olin appears to serve as a shop/circle for them to work under during the Fancy Frontier convention in Taiwan.
EDIT: A final note would be the signatures on the images here and here. Yeah.