Solid Hardwood, Engineered and Laminate Flooring - Carpet runner removed from stairs - problems with uniform staining

Just had professional work on my red oak flooring: spliced in new flooring into existing flooring. Not the greatest job but that's not the problem. To complete the look, removed the carpet "runner" that ran down the center of the central staircase steps (the carpet was on the stairs for 7 years). Which brings me the problem: the exposed, previously finished, wood portion of the step. vs. the newly exposed part of the step.

The staple holes were filled, steps were sanded, and refinished. However, the exposed part of the step differs in shade (deeper, darker) from the center part that was covered by the carpet. You can see the separation/lines in each step. The owner of the business said they sanded each step, getting the entire step to the same level. But because the center area was not sealed prior to the carpet being laid, that over 7 years, it will be different from the exposed portion. Is this accurate? Can the steps not be sanded and refinished so there is no difference in the coloring? What should or can be done? Thanks for any and all help?

Just leaving it exposed as the sides have been for 7 years will eventually blend it in.