Yep. 3% is the norm for AWD or 4wd vehicles. And matching tires is key, i.e. Must go back to the same tire or as close as possible in tread design, speed rating, load index.Per my quattro's manual, tires must have a circumference equal to each other within 3%. A mix of brand-new and worn tires will exceed this limit. The result is driveline stress that exceeds the specifications.
Tire shops can and will shave a new tire down to match tread depth.
My almost 9 years at NTB, tire shaving has never taken place. Perhaps other regions do it, but not around Austin. I believed it was a commercial tire thing mostly.