Rose, there are a lot of different kinds of wood that have been used for floors over the years. What kind do you have?
Planks have been sawn to about any width. How wide are yours? Better floors are made with tongue and groove joints planed or milled into the edges. Do your floors have this? Floors with tongue and groove joints only have so much wood available for refinishing before there just is no wood left. Remove a quarter round or 2 and measure how much wood is actually left. What does it measure?
You may be trying to use a top coat approach when you need to be sure that the wood has what it takes. That's like trying to fix cracks in the plaster while the foundation crumbles away. It just will not work for long. Let's see what the foundation looks like first.