Hi Neil.
Good to see im not the only one that does bad images, not a lot to go off.
Would have been good to see a clear image of the nakago showing its shape.
I see you hoping to date it to the end of the Muromachi period, theres a good chance it is.
Personally, i would not be bothered about which Sukesada made it, let alone signed it, just too much variation. Its not like we are talking about a few smiths at the end of the Edo period. Mass production churning out weapons, not art swords.
Can you see any detail at all with the grain in the steel?, i see some hamon, reminded of something like this.
Japanese sword Touken Komachi, Wakizashi, Shirasaya Bishu Osafune Sukesada
Wish i could be more help.
Cheers