the paint could be hiding a major stain, blemish, or an area that you will only reveal upon sanding.
you are in for a major job and one that is extremely messy and dirty. Be advised.
Your efforts are genuine, as nothing is more attractive than nice stained sealed hardwood floors. For someone to paint them is a "war crime", but maybe its for a reason. 100 years is very old for hardwood flooring, but it definately can be done and I have actually seen it.
But its using a drum sander, then the edge sander, and preping, and all.
Check this out before you tackle the job as to whether your ready for this big of a job.