Holy thread revival batman!
I just spotted your reply Chris! sorry!
No they aren't allowed to do it now, this was actually 1988 when I worked in the hatchery so 26ish years ago.
Back then we were still recycling farm animals entrails back into their feeding etc, the chicken processing factory I worked at minced up all the heads, guts and feet and they were mixed back into the feed for the next batch....
BSE/Foot and mouth etc stopped all that...... things are a lot different nowadays.
The eggs were candled in the first week, I'm pretty sure it was at 5 days and all clears removed and sent to the bakeries, nowadays the options are incineration or landfill.
Unless the egg is cracked or has had the bloom removed from the shell via scrubbing or washing it doesn't "go off" as such, and especially not over a few days.
you'd actually be hard pushed to spot any difference in an infertile egg thats been through a few weeks of incubation provided its shell stays intact, as I mentioned previously we often eat them.
If its cracked or washed etc then its a different story, in the hatchery they were known as 'Bangers' for good reason!