So I did it - turned on the bator and put in some store bought "fertile" eggs from Trader Joe's for a "test hatch".
Not got high hopes for these - they were previously chilled, and then sat at in the basement for 4 days before I got around to turning on the bator.
I have had mixed results with these eggs in the past with from 0-50% hatch rate. The hen that hatched previously was very sweet (but not smart), and was a laying machine.
Chilling isn't necessarily a problem. Cooler temperatures are recommended if eggs will be stored a long time.
What is the Julian date on the Trader Joe's carton?
The date was Jan 20th so they had literally just been put out. That is why I was so tempted to grab them.