Those recommendations for annual changes carry a couple assumptions: 1) dino oil 2) short trips or short running periods that don't properly warm up the engine. These go out the window with synthetics. Can go multiple years. Am on multiple years on the generator and on the Tacoma. These always get warmed up well when used and have synthetic.My new trctor came with 10w-30 and the OM recommended it for my climate. (USDA zone 5)
I just buy motor oil and hydro from the NH dealer.
I also don't do annual oil changes with <30 hrs/yr on each tractor.
I'm running Kawasaki engines on my z turns I've always run Kawasaki oil but in the pass seams like I start getting oil consumption after 600 hours had couple going Thur half quart day I've already got 200 hours on one 350 on one thinking about switching to full synthetic mint of waiting to later or mint not need to anyway
Thought on the matter I've had people tell me 2000 hours and no problems