Statistics for occurrence #1 of “N. S.” in entry massachusetts of Harper's Encyclopedia of United States History:

...ny for planting a settlement, and for funds with some London merchants, they went from Delftshaven to England, and sailed for America from Plymouth in the Mayflower, of 180 tons' burden, on Sept. 17 ( N. S. ), and, after a stormy passage, arrived at Cape Cod in November. Seeking a good landing-place, the company, 101 in number—men, women, and children—did not leave the vessel until Dec. 22 ...
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