Our house was built in the 1890s and has the original wood floors in it. These floors were covered with subflooring when we moved in. The previous owner jacked the house up and redid the foundation along with covering all the flooring (and many other updates). I have removed all the subflooring on the first floor. The original flooring I cannot tell how many times it has been refinished. It does not have a subflooring of 2x12 unfinished boards which I have seen in homes built in the early 1900s. So it lacks that support and it can be loud. My dilemma: is it too thin to refinish? Should I just scrub it clean and wait until I can afford to put in all new flooring?
If sanded down, it will be gorgeous!. All you need to do is to find a gap, or check many gaps in the flooring. Use something thin like a credit card or thinner and shove it in the gaps. If there is 3/16" of depth to the surface, there is plenty of room for sanding.
I have seen in an old home the floor sanded down so far the tongue was exposed in places (0" depth), still looked good and the owners kept it.
I refinished a floor of similar age - big cylinder sander, diagonal passes etc etc.
Came up beautiful - remember to punch down every nail 😀, otherwise new drum paper required…
Make sure you dust seal the area, the dust gets EVERYWHERE. Wear dust masks.
The final result will depend on what you start with - I had loose boards, some damaged etc so fixing and swapping positions worked for me. Good luck.