What happens if We_Are_a_Cool_Group has translated chapters 1,2,7,9, and 13; ABunchOfFatAsses has translated chapters 1,2,3,4,5,6,7; and Drunk_Again_Damnit has translated chapters 5 through 12? (I've seen such situations more than once.)
In theory, you could just make it the responsibility of the user to manage such situations, but a lot of people would be bit by not noticing that the translations of a given series were characterized by such gaps and overlaps.