Some saws are not eligible for the Double the Warranty. IE. The MS 194T or the 200T. These are Professional only saws.
If your dealer can register it on- line /In-Store (at the stores computer terminal) it will let you know right then and there that the saw is eligible. You have to enter that it's for "Home Owner" use and the next step will ask you if the customer bought the oil or the gallon of Moto-Mix. If you purchase a top handle saw, you will never get that chance. (Top Handle saws only have a 3 month warranty)
If you input that you are a Landscaper, Business, Government... etc. you will not get the chance to enter if you bought the Ultra oil or Moto-Mix. Again.. Homeowner only.
You can still get the "double the warranty" from the dealer if he/she enters that you bought the oil and really didn't.. same if they know your are a logger or a tree arborist and input "Homeowner." Stihl doesn't check the receipts. They rely on the dealers.... I imagine though if you get caught doing this too many time you can lose your Stihl license... that would be bad for the business.
I'm pretty sure your MS 500i is eligible for the Double the warranty as long as your a "Homeowner."
I know that a MS261 C-M and a MS 462 C-M, both "Pro Saws" are eligible for the Double the warranty.
The dealer can delete your registration and re- register it for you and correct that if they are so inclined .. if they don't... then I would call Stihl and let them know the situation... Maybe your salesperson just needs an education.. but that option should have been made available to you at registration.
The official wording is "Double limited warranty protection applies to select STIHL gasoline-powered products purchased for personal non-income producing, household purposes only. "