For a few weeks, we have been buying regular small boxes of oranges
from the local coop, described as 'grade 1 easy peelers' - Spanish
mandarin.

Having a sweet tooth, I found them quiet juicy and sweet though not
entirely consistent even from the same box. The last box contents was
different, not so sweet, not so juicy and very pithy, not nice at all
so they were binned. The obvious difference was that they had a lump
where the stalk goes, bulging rather like nipple. Might that suggest
they had been picked too soon, or simply a different variety?