How the floor is sanded can also be a factor in sheen appearance.

Hmm, none of these seems applicable to our floors. The original floors were all sanded at the same time, and with the same method. Sealer and poly were all applied the same way across all rooms. They were satin-y from the start, except for the one area (a strip in front of a bay window). It was a dry/dull sheen from day 1 in that one spot only.

The new floor was sanded the same way as the old floor: drum sander, then orbital, to 120 grit.

Would photos of the rooms help? I don't know that I can capture the sheen real well, but perhaps there are some other clues.

There's a chance that the duller strip in the old area has no relation to the duller new area, unless just that strip was done with a bottle from a different batch (different from the "old" finish and the same batch as the "new"). Was the dull strip done first or last? It could be the effect of a holiday, sunlight on the floor or over-working the finish.

Possibly the finish being few years old could be a factor. The effect of air moving across the floor white drying, temperature and/or humidity could be a factor.

The dull strip in the old area was done all together with the entire old floor. Same batch, same time, all contiguous.

Here's a photo I've got on hand. The dull part is under the window on the left hand side.

Here's a photo of the "before" floor, from about the same angle, right after we tore out the carpet.

I understood that so it doesn't change the intent of my comment. Perhaps I should rephrase my question. Was the duller strip done at the start of the coating job or at the end? Is it in an area where the sun shines on the floor? Is the duller area at the perimeter or does it extend out further into the floor? Does it align at all with the direction of the floor or is it parallel to the wall? Again, I'm not sure that this duller area has any relation to the duller nature of your newly finished area.

Sorry for my delayed return/response. Because of the diagonal layout, I started applying the sealer and poly in one corner with the short piece, and worked my way out, brushing along the lengths of the boards, getting wider and wider. So the duller portion was roughly in the middle of the process. The duller area is a rectangle, roughly equivalent to the bumpout space. I remember when sanding it the wood seemed different than the rest (though not literally so, as it's extensions of the planks).

I agree that I don't know that the new room vs. patch in old room are dull for the same reasons. I just mentioned it because when I described the finish in the room addition I remembered the dull patch in the dining room.

The reason I asked is because I've seen floors where a portion of a perimeter was brushed, then when the center was applied with an applicator, the sheen on the edges were often duller than the field.

Ahhh. No, this wasn't the case. I hand-applied the entire floor.

I got nothing....