The gutters don't seal between the roof and the fascia. However, there
is a small vertical board on the attic side of the gutter. It doesn't
seal, as such, but no light comes through from the outside.

The upmost side of the soffits can be seen from the attic, again with
no obvious light coming in. The bottom of the gutters can be felt as
they span between the joists in the attic.

There's no obvious movement of air in the loft, even on windy days
(though I'm not saying the loft is hermetically sealed).