Well, I’ll be dammed.
Can I quote you on that? 
I ain’t proud.
…or tired.
Excellent pick up on the AG reference. Must be that time of year.
If they happen every few days, then is it that ‘unusual’?
The quote on the linked page is:
An explosive device and a suspicious device are two different things. I heard of suspicious (i.e. unattended) backpacks, lunchboxes, briefcases, etc. on the intercom (when I worked next to a plutonium facility) on average of once a month.
That may just be the definition of how they define probability (likelihood). An example of a risk matrix would include, normal, anticipated, unlikely, very likely, and improbable. Improbable events might happen once every million operating years, while a normal event might happen every ten operating years.
ETA: Scratch that, that’s for a facility. It was defined as unusual by the NRC, which oversees many facilities, and even if such an event only happens once every six months at a facility, the NRC may see these unusual (facility) events once or twice a week.
It was later confirmed to be a “viable explosive device.”