I have been drinking this for about 25 years and always found it consistent. I have bought it in 3-4 different states. Are you sure that who ever is pouring it for you is actually giving you MM?
A few months back, MM announced costs & demand were going up so they reduced the alcohol percentage to keep the price consistent, and justified/observed that some people favored competitors’ wares because of their lower proof. The outcry was enormous, and after making the diluted formula for a while decided to reverse course. Some of us took our $$$ elsewhere for want of consistency.
https://www.google.com/search?q=maker’s+mark+scandal