I'm not sure who determines what a shorty plus is for what show because shortys aren't my breed.
But lets pretend I've never heard of or seen a shorthorn plus before. If someone asked me what one was I would say its a shorthorn plus some other breed. It would have to have a significant % of shorthorn because its the base for the breed name. 50% or greater is the majority so its shorthorn plus ______. Say you've got a shorthorn plus with papers but its 25% shorty, 55% simmi, and 20% angus. Would you call it a simmi plus or a shorty plus bc the shorthorn association will let you register it.
p.s. I don't know what the registration requirements are so my numbers may be incorrect. It's also getting late so I may just be thinking about things too hard.