What I read and have been told is:

1) Versions were customised to things the singers knew, the ones we have are just a snapshot.
2) the "pulls" were dependent on the work to hand. See Bunty shanties particularly for illustration.
3) the songs lasted as long as the the work. They didn't sing on if there was no more rope.
4) look at Stan Huill videos and you will hear fewer words eg We now sing "Ranzo me boys Ranzo" - while he is preserving breath and making the rhythm more explicit he sings "Ranzo boys Ranzo". He on the down pull (one of three strands - think pulleys) and two (no more) are on the tail rope.
5) the point of shanties was to get more work out of less men - so there weren't huge gangs.
6) Stan Hugill states that his printed versions were camouflaged (ie bowdlerised) due to the mores of the day.