When you say 'sorting labels' do you mean the order in which they appear in the front end component? Or in the back end config?
IIRC, the out of the box default is alphabetical (its been a while tho) but a developer can customize to be listed by number of times that label has been applied to content in the UI.
Nothing I'm aware of for sorting in the backend config tho (which can be messy! lol)