This is a recently published volume - not part of the circa 1900 Massachusetts vital records project - and thus is not out of copyright and is generally not included in "Massachusetts to 1850" vital records collections.
The explanatory notes for the American Ancestors (NEHGS) database states:
Only half of the vital records to 1850, from the Plymouth Town Clerk's books, have previously appeared in print. These records are from volume one and part of volume two and constitute the first 318 pages of this book; they were taken from literal transcriptions by the legendary George E. Bowman, in The Mayflower Descendant quarterly magazine. We have compared his work to the original records and found his accuracy impressive; few discrepancies were of enough significance to warrant correction.
Dr. Lee D. van Antwerp transcribed the balance of the vital records through the year 1849 from microfilm prints of the Town Clerk's records to form pages 318-649. His work was meticulously compared with the films and corrected as needed. These additional records are from volumes two and three, and from the Register.
The appendix contains a few records copied from the published Plymouth Colony Records, some of which are identified as belonging to Plymouth people.
All names in the above records are included in the index, which we believe to be a most significant part of the present volume.
The names of persons and places have been copied exactly; Middo. stands for Middleboro, Plymo. for Plymouth etc. All other spellings were modernized. Standard capitalization has been used for clarity. Dates are not changed from old style (O.S.) to new style (N.S.); those which were recorded, for example, as 17011/12 are printed here as 1711/12. Words which were crossed out in the town books are struck through in the printed text. Marriage intentions have been shortened somewhat and, usually, an asterisk and footnote have been used on those pages so that the intentions will not be mistaken for marriage records. Birth records in early years often listed both parents with the family surname (e.g., children of Nathan Ward and Elizabeth Ward his wife), which does not mean that the father and mother were born with the same surname. On items of doubtful interpretation, the editor and proofreaders have checked with each other, with the original record books, and with the 19th century copies made by Nahum Mitchell around 1840. Any items of which we are still unsure carry bracketed comments.