its the rented grazing issue
if its scotland the sheep are registered to the holding regardless of who physically owns them, in england its slightly different as the owner can get a holding number on the landlords land effectively...
i spent forever working this out when i got mine as in effect in scotland any sheep on rented grazing belong (in the eyes of the government) to the landlord...
it made my head hurt then as well, think i may need a lie down now...
ps for scotland i have now had this confirmed from multiple sources...