I had too much coffee today so I thought I'd add a few thoughts on NE rifles.
First, much of the style of analysis applied to Pennsylvania rifles is not transferable to New England where Worcester County was the only major center of production. All of the brass bits, especially patchboxes and trigger guards appear to have been supplied by wholesale distributors. The variations are usually minor and have little to do with the maker in any case. If, as I believe, most were made to outfit militia rifle companies, they were made in batches and, not surprisingly there are cases known of more than one nearly identical rifle marked to the same company (though this is rare). I have a John Mason that is marked under the barrel and in the barrel inlet with the roman numeral XXXII - suggesting there were at least 32 guns in the batch. I had a very late Henry Pratt, made as percussion around 1840, with the numeral 62 on the patchbox lid. There were 62 privates in a Mass militia company at the time and this rifle was nearly unused which suggests, as the highest number, it may never have been issued.
The period of manufacture for the NE rifle is also much shorter than for the Pennsylvania rifle. Realistically it extends from around 1800 to 1842 at the latest. In 1842, as part of a reorganization, the state furnished arms to the militia (something it had never done before) and the requirement that every male citizen from 16 to 60 arm himself was allowed to pass into non-enformcement (I think it was actually repealed in 1912) so we have a limited use for a shorter period of time. The result is that true NE rifles are far more rare than Penn / southern etc rifles though this isn't obvious because they have also attracted very little collector attention.
There are exceptions however. Welcolme Matheson is one as we've already noted with his very different style of stocking. Holbrook used a distinctive eagle escuthceon on the wrist of some of his guns and a silver escutcheon with a so-called "bow tie" design is said to be the mark of the prolific Allen family.
But much of this is still conjecture. For my own part, since I like them, I'd just as soon they never attracted much attention. If they get too expensive I won't be able to collect them so the fact that they are pretty much overlooked is just fine in my book.
Joe P