It is my understanding,and we have a Dave's manager here on the forum,that they buy them precooked from a central commissary and finish them in Cookshacks at each site.
Sadler's is one Tx firm that supplies to many chains,box stores,and restaurants.
They can add smoke,at a temp around 200�,and bring to a serving temp below 160� internal.
A rest/hold in a warm smokey beef broth is standard for many prepared meats in restaurants.
This works from burgers on up.
Just a guess,and maybe someone more knowledgable can add to it.
I have eaten at some Dave's and they have a nice restaurant experience.
As far as personal preference,I don't know any brisket cooks that don't far surpass them.