Chet, its good to ask, but those types of records are rare, very rare. Vital records in NE (& NY & NJ & . . .) are a wonder to behold but are VASTLY incomplete. If you run searches through the databases at Ancestry or at AA-NEHGS and get zero responses, if you review all the Snow genealogies and you find nothing after his birth -- that is, silence -- you must assume that John-12598 died young. Unless you can demonstrate he appears in his father's will (if there is one) or in some real estate transaction involving his siblings, then he died young. Which is what Tom Allen is pointing out regarding the "silence" about him at M5G 6:64. His "line" is not carried forward because those researchers could find no evidence that he survived to marry.
In addition to the importance of the naming pattern that Ashley Jones points out above, there is also the GEOGRAPHICAL pattern. People don't move around within NE all that much at this time. Cape Cod people are most likely to move westward and southerly into Rhode Island and into eastern Connecticut. It is highly unlikely a Cape guy gets into NH, stopping to marry a Marlborough girl on the way. I'm even surprised a Woburn guy did that in this time period, going north, that is. Another Woburn family, the Moses Cleveland descendants (large families & very mobile) first moved south into Freetown & Bristol Co. & RI, then say after 1730 started expanding into central Mass., pushing west until they got through NY State to, yep, Cleveland, Ohio.
To sum up: (1) repeated use of unusual male name strongly indicates direct relationship; (2) very reputable research very strongly suggests alternate person died young; (3) NH is much further away from Truro than it is from Woburn, no matter how attractive the land deal might be for a younger son in an extremely limited land situation.
Oh, a (3b). While Truro men as sailors in the local to NE coastal trade are going downeast to Maine and will stay, you can't sail to Marlborough. You have to walk. And, again, Woburn is a shorter walk to Marlborough than is Truro.