I suppose the difference would be whether the supplier in Maine merely
orders their seed from some other commercial suppliers or whether they
harvest seeds from their own field trials. If the latter is the case,
I think it would matter.

You may not realize that there is a hierarchy of seed for commercial
distribution. While the details vary somewhat from state to state and crop
to crop, in general there are three categories of seed:

Foundation
Registered
Certified

Certified is what is ordinarily used for growing a crop, and is the least
pure of the grades. Registered is more pure, foundation is still more pure.
Foundation seed and registered seed can only be produced from foundation
seed (leaving aside for a moment the process of creating and releasing a new
variety), and certified seed can only be produced from foundation or
registered seed.

Because of the very high cost of producing foundation seed (due to the
isolation requirements and manual labor involved in roguing out off type
plants, and the testing costs, and the risk that the resulting crop may not
meet purity standards for foundation and have to be sold as registered
anyway), it is ordinarily produced only rarely. Foundation seed is stored
in a controlled environment and used to produce registered seed for many
years to come. Because of its value, foundation seed continues to be used
even when its germination has declined to as low as 20% or 30%.

So you see, the certified seed you buy is at most two generations removed
from the foundation seed. That does not provide much chance for genetic
drift, particularly since off-type plants are still rogued out by hand in
registered and certified plantings.

Typically the small-scale seed grower obtains registered seed from a company
that specializes in a particular crop, and then grows it out to produce
certified seed. So, more often, there is only one generation of
localization that occurs.

--
Sam