Yeah. The ready-mix operator usually also runs the quarry, and they have no problem understanding proper aggregate base sieve analyses when they are selecting their quarry sites. They fully know how to mix and select their media.
Only exceptions are possibly a larger business operated by brethren who aren’t held accountable for learning their business. Instead they might swing deals with dredging operations for inexpensive sand.
I tend to prefer the small owned businesses which are kept clean and well organized, manifesting they are giving you an efficiently operated product at a competitive price.
In much of the midwest where my experience is, the sand is bought from a sand pit and the ready-mix company crushes limestone from a separate quarry operation that is often owned by others. The ready-mix plant should have bought this in their testing of mix designs.