My question is if a restaurant is ordering meat from a purveyor, how can the chef if at all control tenderness and know whether his dish is going to cut like butter or not? What can a cook do to meat to make it tender before service without knowing if it were to be tough or not?
A good cook nearly always knows whether or not she's working with tough or tender meat. There are questions of touch, marbling, grade, cut, etc., as well as familiarity with the next guy up the chain -- whether he be butcher or wholesaler.
There are techniques which can make a difference, like jaccarding or marinating, cooking sear and blast or low and slow, dry, braise, poele, etc., but they are chosen depending on the quality of the meat to begin with, and its presumed suitability for a partciular dish.
And even then...
For instance, I'd smoke a Prime, Choice, Better than Choice Angus, Americah Black Face or even a Select
brisket with pretty much the same prep and at very similar temperatures -- but would expect my results to be more or less consistent with the grade. Also, I'd smoke a standing rib with the same rub as the
brisket and at the same temperatures, but I'd pull the rib rare (125F, or perhaps a bit less), while taking the
brisket "past done and into tender" (never less than 192F).
BDL