My house is about 103 yrs old and has the original pine floors. I've heard you can only refinish a floor so many times and I have no idea how many times these have been sanded down. They're not in great shape but I really can't replace them right now. Is there any way to tell whether or not I can refinish them? If it makes a difference, there is no subfloor.
I would try sanding in an inconspicuous area of the floor and see how it comes out. As far as trying to see how much of it got sanded you would have to somehow look at the end of the boards and see how much you have left to sand before you hit the tongue and groove and even that is not going to be accurate because when you sand a n old floor you usually can't sand all the way to the edges because of baseboards or other moldings used.