Hello. We had the 94 year old floors in our new house refinshed and stained. We had some chatter or wave marks (not sure the difference) upstairs (semi-gloss finish), which the refinisher said was a result of boards not being secured to the subfloor. On the main floor we went with satin finish and chatter marks were better but not eliminated. Our bigger concern is a four foot "puddle" in the dining room where the stain is lighter than the surrounding area, with a line around the perimeter (see picture below) Are these lapmarks? The refinisher said he sees the issue, and says the only way to fix it is to resand. We did not discuss whether he was willing to do this or not.

The DR flows to the foyer and living room. We are also aware that with these old floors there is a limit to how many times they can be resanded. Questions: Should we require the refinisher to redo the dining room (part or whole), or are we risking even worse results trying to blend into already finished areas? Should we consider hiring another refinisher, or are these issues a result of the age of the floor (vs quality of refinisher)? Would another reputable company ever be willing to 'fix' the mistakes of another refinisher? Any advice is appreciated. See pic below.

https://www.dropbox.com/s/bk0tsxtti5dk2 ... s.JPG?dl=0

Sorry the floor didn't come out more uniformly. Sometimes the stain can be lifted when applying the first coat of finish because it had not had enough time to harden before finish was poured on so it could be spread around. Since the color is not as intense in the spot becuase some has been "washed off" it will be very difficult to have the color look perfect unless the whole room/rooms are sanded again. Was the floor cold between the staining and the first coat of finish?
There may be people who would try to blend the spot in with a tinted finish only in this area, then coat the whole floor again to make the gloss level the same, it would probably be noticeable to you since you have already noticed the area.Then again it may look worse!
If this is the reason why there is a light spot, then another sanding and refinishing would look better, assuming that more dry time takes place before the first coat of finish.
I don't know of any contractor who would accept a job like this because once you take over another's work you will be responsible for the whole area.
As far as looseness of the sub-floor I always recommend fastening loose spots before the sanding has started, which would be noticeable when making the inspection of the floor during the visit when the estimate is made. I always expect that an old floor will need some "repair" which includes addressing squeaks and loose butt-joints. Most contractors will skip this step for a couple of reasons.
Without seeing the whole floor, if this is the only complaint then I would recommend accepting the work "as is". Over the first year the whole floor will develop a patina from light penetrating into the wood fibers and getting a little darker over the whole floor. Even indoor lighting will make this happen and the floor will become more uniform and much less noticeable.
Your contractor does the best that he knows on each job. Sometimes things don't work out perfectly. Experience will allow better judgement. Sometimes a contractor will use the exact technique from job to job without recognizing a factor that may spoil their work.