did not have any sealer or protectant finish. They were oiled periodically to keep the richness and beauty. I worked in an old downtown JCPenney store during college in the early 60's. This store was built before I was born and it had hardwood floors.
I remember every Saturday night we had to sweep, mop, yes wet mop, the flooring and then spread some sort of oil all over the floor and work it in with a mop also. We were told to mop or work it in in the direction of the grain and walk or work your way out the front door. Then next Monday, as we were not open on Sundays, the floor was like new and not slippery at all. It was really beautiful.
You can still do this work if you want, but its not necessary. The oil in the wood probably made the wood last as long as it did.