My choices are:
#1) Trace the family trees of each of the identified burials backwards in time to the settlement of the town. The subsequent step would be to move forward in time to identify extended family. My reasoning is that families were buried together and that more members of my identified families have the greatest odds of being found at the Brigham site as well. A wide range of sources exist, from historical publications to documented genealogies.
#2) Go back to the founding families of Marlborough Plantation and trace their lines forward through my research period. (All three towns being researched were originally part of one single “plantation.”) The thought is if they lived here, then they died and were buried here in one of the 3 towns, including our Brigham site. This approach, while theoretically creating a large net of possible burials at Brigham Street, is the most time consuming method and isn't efficient in narrowing down possible burials there. As with method #1, a wide range of sources are available with this information.
#3) Locate documented inventory lists of the early colonial burials in Marlborough, Northborough, and Westborough to use to identify in which modern town early settlers resided. Historical documents from each of the towns may still exist and be obtainable from reliable sources. Death records for Massachusetts up to the year 1849 have also been published and are easily accessible. The following step would be to locate each of the recorded deaths from Marlborough, Westborough, and Northborough in any of the cemetery burial inventories. Unlike the other two methods, the evidence for this research task has already been researched and documented by others and I do not need to reinvent the wheel.
In summary, the most critical factor in moving forward with research will be to have the list of burials in nearby old burial grounds to refer to as ancestors are identified. Once I have the known deaths and burials for reference, I can decide how to approach the unknown burials.
LESSON LEARNED: Work from the "known" to the "unknown".