When I started quilting nearly 35 years ago, I washed everything and required my students to do so, too, because the finishes bothered me so much. As the years went by I bought too much fabric to keep up! I didn't want to waste time pressing all that stuff, so I started taking an anti-histamine almost every day on doctor's advice, and gave up "sweating the small stuff".
I still have some of that 30+ year old, pre-washed fabric in my stash -- used some of it just yesterday -- and have never given a thought to whether it would play nice with the 'dirty" stuff. Guess my fabrics have been well trained over the years, they behave 90% of the time.
Jan in VA