It was easier a few years ago. The Mitsu built tractors sold by Mahindra were built entirely by Mitsu, including engines. Shipped to the USA where the tires, roll bar, steering wheel and sometimes battery were installed. Spec'd out by Mahindra, Mahindra color and so forth. TYM, same thing, except TYM has always used someone elses engine, Daedong, Yanmar, etc. When the Tier IV thing happened, Mahindra developed it's own solution with a new common rail engine with no DPF. On tractors over 19kW, the Mahindra engine was a very good choice. Mahindra shipped engines from India to Korea and Japan to be installed in the >25.48 HP size, up to about 75 HP. That muddied the waters a little as far as making this explanation simple.
But regardless of the builder of the engine, when the tractors arrive at the USA DC, they are complete tractors, less the items I have already mentioned. I've been to many of the plants overseas personally, and I owned the very first independent distribution center for Mahindra. Now all of the DCs are independently owned except for the big one in Texas at the USA HQ.
Nothing wrong with rebranding or rebadging. A lot of John Deere's excavators are built by Hitachi. A lot of their small tractors have been built by Yanmar. Most of the majors do this.
Kubota pretty much builds there own stuff. I believe early on Kubota had a Fiat derived orchard tractor and there may have been some other minor collaboration, but far and away Kubota is a manufacturer of their own product. I see that as a good thing. If there is a design or product quality issue, fingers do not need to be pointed outside the walls of Kubota.
Branson is similar to Kubota, but a ton smaller, in that they make most everything on the tractor. Even the Cummins A series engines are built by them. I think Kioti is pretty much a sole source tractor as well.