The rank insignia on Joe & Bernadette's collar points change positions from one scene to the next. They have yet to be worn properly.
Some interior shots of Joe driving the GMC SUV show a steering wheel that was found in the 80' Chevy S10/Blazer/Astro van.
Leaphorn's motorcycle has low bars but in one shot it has semi ape hangers.
Numerous vehicles throughout the series are seen wearing white lettered radial tire. While radial tires were relatively new in the early 70's, varieties such as the Goodyear Eagle ST and BF Goodrich Radial TA weren't available until the 80's.
The Buffalo Society use of a painting to move the money to Devoted Dan doesn't make any sense. Doing so opened them to the possibility that the painting could be lost, as it was when the Mormon family bought it. It also ran the risk that the shopkeeper, or someone else, would notice them coming in repeatedly to buy the painting, that someone at the car dealership would notice someone repeatedly handing over the painting, and require them to pay the painter hush money. They could have just brought the cash openly and directly to Devoted Dan.