What I heard on the radio this a.m. was that today (Jan 20) in 1956 JD intro'd the "20" series tractors. I'm sure the "x0" tractors were still available. Back then, dealers inventoried tractors, like car dealers. So, if they intro'd the x20 tractor in mid-Jan, I'm sure they sold the 50-60-70 tractors thru summer. Our local dealer sold a 730D at the same time he sold a 4010D. We own a late 4020 that was sold (1st time) AFTER their initial 4430 tractors arrived @ the dealer.

So, you could be right. I googled & found this. Don't know if it's authoritative or not. But, we did own our 720 in '56. I don't think the ad photos show though.

A New Three Point Hitch A new 3 point hitch was added in 1953 for the 50, 60, and 70, with a large range of new implements to make pick-up-and-go farming easier. It was the first North American introduction of the Category 2 hitch which later influenced development of a new ASAE-SAE technical standard.

	NEW STYLING What would become arguably the most popular John Deere paint scheme.1956 saw the release of a sparkling-new, two-tone color styling FLOAT-RIDE SEAT Absorbs shocks and tractor vibration; makes rough fields seem much smoother. This new seat is fully adjustable to your weight and height for maximum tractor driving comfort. INDEPENDENT PTO Delivers full power of the great new engines, completely independent of the transmission clutch and the hydraulic system. Convenient pedal control.
John Deere Brochure View John Deere 520 620 720 Tractor brochure