Office update
T.B.O is a recommendation. As long as you fly within the set of regulation you are legal and legality is the point.
If you fly FAR135 = Public Cat. You can operate your engine to TBO + 20%.
If you fly FAR91 = Privet Cat. you can operate on condition.
My engine is 2550h SOH and it is legal to fly, it is on condition.
Once I was told that there is a company in Jersey that operates Trilanders and run the engines up to 5000h (they change cylinders every 1000h) with the permission of the CAA. I also heard that Oxford operate their PA28-161 to 3500h. also with a permission.