Most early GN bricks came from Lincolnshire (the GN purchased a works to ensure supply), even as far South as Sandy the bricks are not local and are similar to those used on the original line.
It is likely those cottages were built at a slightly later date using locally sourced material and given the GN's preference for spending money on track and not buildings it's unlikely that any stone used is Bath/Portland, as even then it commanded a premium. The use of stone in the cottages would have been for construction rather than decoration, and to keep costs down some of the walls could have been single skin brickwork too.
Edit to add, in photographs what can look like dressed stone is actually any old stone/timber/metal that was strong enough, but then rendered to weatherproof.