The best thing is to take recognized slips out of the flock as soon as they start being recognizable with reddening of comb/wattles. When there's any question, keep a close eye on their behavior.
If they start crowing or competing with roosters, they're obviously "slipping away...."
The...
Just ate a portion of a Jersey Giant slip that I processed 2 days ago. Don't have the weight, but the chick arrived in the middle of last September and was caponed in November.
When processed, he had _one_ very large testicle (1 3/4" long) and a full comb and wattles. He was "arrested" while...