Grandfathered Building Lot? Massachusetts property contained 3 lots..

[Jurollo]

I recently purchased a home in Ashburnham, MA which contained 3, seperate 8800 sq ft lots. The house, sitting on lot #3, uses town water and sewer. Based on current zoning neither lot #1 or lot #2 would have sufficient square footage to be considered a feasible building lot, however, to my knowledge these lots have never been merged. The question is one that I will ask in a more general manner rather then one specific to Ashburnham, MA. Do grandfather clauses generally apply to lots with no structure currently on them or only to lots with structures currently located on the lot?