As with many dances of ceilidh origin, there are several variants of the "Cumberland Reel".  In the RSCDS version (Book 1 #11) the figure "dance down and lead up" is 6+6 bars [bars 17-28].  The cribs and diagram show this version.

In one variation, this figure is 4+4 [bars 17-24], which is easier to dance.  Then "all turn partner RH" is added at the end to fill in the missing 4 bars.

In some versions 3c+4c also dance "RHA ; LHA" for bars 1-8.