The New England states, other than Massachusetts, adopted a statewide system of collecting vital records (birth, marriage, and death) in the late 19th century. [Mass. was first in the mid-19th century]. After those dates you should be able to find any such record in the statewide system. Usually, the state official asked that the town clerks to submit their records for previous years as well, which was done on a voluntary basis. So, in Maine you have a pre-1892 statewide collection that includes some but certainly not all towns. Vermont has a collection of vital records pre-1870, etc.
New Hampshire has a similar set that has been microfilmed. It functions the same as the others. Some towns are included and most are not. However, New Hampshire is unique in that its order of surnames is not alphabetical as are the records of Maine and Vermont. New Hampshire alphabetizes the surnames by the first letter, then third letter, then second letter. So when searching the name Wallis or Wallace, it is WLA. It is therefore after names like Wright (WIR). It is very confusing to use, even when you've been using it for twenty years.
New Durham is one of the town that did contribute to the statewide pre-1900 vital records. However, the town clerk just took the records, copied them and sent them in. So marriages that were only bride and groom on a ledger, look like this.