The never-finished wood is going to be lots darker than the recently-refinished floor. It's chancy to try to bleach the old wood lighter. You can't achieve lightening with a lighter stain; you can only add color with stain, not take it away. If you try a bleach, you can still stain everything later should it fail.
Casey

Use whatever finish system was used on the rest of the floor. However, the fact that the unfinished wood was exposed to room air and little light will probably make the result a little noticeable but acceptable.