Okay, it's been six years since I worked on the farm, but when I did we had new, state of the art tractors and telehandlers, none of them had an immobiliser, and none of them had unique keys.
The only immobiliser I ever encountered was on a 1997 JS200LC tracked excavator - and that was an aftermarket jobbie which was next to useless
A JCB key fits all JCB's, a case key fits all case, a Valtra key all valtra's, likewise all of the other brands.
Have a quick look on eBay at the amount of sellers listing "plant key" and "farm key" bundles where you get one key for each brand. Machinery is all keyed alike. Any of you that think tractors or plant is hard to steal needs to think again