Thank you very much for all your answers.
This information is extremely helpful.
I didn’t know that a wakizashi could also receive an official cutting test by Yamano Kanjūrō Hisahide, so it was very interesting to learn this from you.
The fact that the mei matches other documented examples of Nagakuni, and that the test is dated to December 1665, really helps me understand the history of my blade.
Since a two-body official cutting test (futatsu-dō kiriotoshi) on a wakizashi seems to be rather uncommon, my sword might be a bit rare.
I know you only saw the tang photos and not the blade itself, but assuming the wakizashi is in very good condition, with a healthy polish and a clear hamon, would you have a rough idea of its possible value or price range?
Thank you again for your time and for sharing your expertise.