I think there are also massive differences beyond the obvious between hauling and heaving chanties. They almost cover overlapping different eras and have obvious structural differences. This is only an opinion but I think the heaving chanties had more stable texts despite the leader having longer to think up the next line. The fact that some hauling chanties appear to have a stable narrative or catalogue structure is more down to the published edited versions than what was actually sung and improvised. I'm thinking of Boney, Whiskey, Reuben Ranzo and perhaps a few others. On the other hand chanties like Sally Brown which are amongst the oldest have had a much longer period to evolve some stable stock verses.