Checking advisories process isn't efficient

We're checking advisories twice a week according to our process However, I've found that we're in risk to repeat same work twice.

One of our sources is NVD RSS feed. However, we can't trust added_at dates we can only rely on unread items. However, as right now we're doing this task with @fcatteau in rotation, we're in risk repeating checking same entries.

This is the state of unread entries after I checked advisories today

/cc @gonzoyumo @fcatteau