Avocado is a one-seeded berry. The papery membrane surrounding the cotyledons
is seedcoat. In the Mexican (Persea americana ssp. drymifolia) and Guatemalan
(P. americana ssp. nubigena) races, there is a single seedcoat. In the West
Indian race (P. americana ssp. americana), the coat is separated into two
distinct layers. But I've never heard anyone suggest that the outer one is
endocarp.