Assuming the label sheet has an even number of rows, after propagating the
labels but before completing the merge, delete the «Next Record» field from
the all but the last label in every two rows; that is:
Row 1: omit «Next Record» from all labels
Row 2: «Next Record» in last label only
Row 3: omit «Next Record» from all labels
Row 4: «Next Record» in last label only
and so on. Since these labels seem to have 10 and 20 rows, this should be
feasible.