I don't believe any state could have a 12,000 lb limit IF you have an axle and tires rated at a heavier rating.
My steer is rated at 20,000, tires at over 18,000, and I've been over scales possibly in every state except Maine.
No problems.
I probably never get over 14,500 on the steers.
A 14,600 axle is what I'd spec if I were to build a new DR.
The factory will put the properly rated tires on the axle.