For some reason Skitch has troubled me for a month or so not reseting the monthly limit, even though Evernote correctly reports a fresh space of 60 MB.
I've tried log out Skitch and Evernote, quit the apps, restart MacBook Pro and log back in Skitch and Evernote. No luck.
I'm using OS X Yosemite 10.10.5 and Skitch 2.7.8.
EDIT 26.11.2015 I've reported a bug.