Most of my answers have been listed here: except there is a specific recovery protocol for the 5/3/1 program. If you do it right, you will be on track.
Overtraining is a catch all term; like "tearing a muscle". Few people who have a "torn hamstring" really tear it off the bone. The "overtraining myth" sells shit and makes people think they are hardcore or whatever. it's Internet Points.
99.9% of people who lift don't compete, are regular guys and have a real job, family, etc. Lots of potential for stress so you have to put things into place to manaage this. Thus the TM, PR sets, teaching people about bar speed, 7th Week Protocol, Joker sets and how we program all of our 5 cycle training - it's almost impossible to fuck up the program if you follow the rules.
"You have a client come in twice a week that you have been familiar with
for some time. Outside of his training sessions with you, in which you
do either squats or deadlifts, he works out three more times a week with
weights. He claims that the extra work is not impacting his training.
However, for a few weeks now he has not been able to move the same
weights and he tires easily. For this scenario, we are keeping in mind
that he has NOT been using any variation of 5/3/1."
I, nor anyone who is a professional, would touch this person. What's the point of training someone if they don't do a thing I ask? I had someone that tried to train with me and also work out at school - I told him he can come into the weight room but I refused to coach him. It's a complete waste of time and effort and honestly, disrespectful.
So to answer your question:
We have indicators and we plan - just like every professional in this business.