The sha512sum.txt file, which contains the signed hashes of "all" the squashfs images, has not been updated since last week (2015-05-16). This makes it impossible to verify the images that were generated since that date.
The most recent snapshots in the file are:
the squashfs generation script is buggy and I may disable it entirely soon.
that has the code for generating the snapshots, I'll cc mgorny to see what he wants done