The labels do not have the inscription "NEDERLAND." This is an indication they were never valid for postage. They were issued locally. "Last Dodo" describes the Leyden one as local carriage label. I am not aware local carriers were legal in the 1970's. So, I doubt that. They, probably, were just adornment.
Both sheets commemorate Dutch victories in the 80-years war (1568-1648) during which the Netherlands revolted against the Habsburg kings that ruled the low countries from Spain.