It most certainly can. Some of your old floors may have been covered with a rug, affecting the patina that was subsequently formed.
I'll stick with the opinion that all of it is longleaf pine, even in the kitchen. I may be wrong about the kitchen, despite your further description. That new flooring hasn't been affected, long term, as the rest of the flooring. See below for drilling recommendation/test.
Yes. What you have further described is consistent with longleaf pine, which is the very assets that made it a flooring material of choice. Additionally, to those descriptive aspects, are the rays seen in the wood in all but the kitchen pics (can't see, that, close/well enough)
In an inconspicuous area, with a 1/8" drill bit, drill 1/8" down, clean the bit of "contminated" cuttings, then continue to drill into the center of some boards for a sample of non-contaminated wood. Smell the drilled cuttings. Those small drilled holes can be easily filled with no damaging/unsightly/or otherwise negative effects.
If you can, determine what kind of lumber the joists/beams/etc is, what the flooring is nailed into. Often times, the same lumber was used for floor framing/support. I may get debate on this matter, LOL, but I'm looking for pine lumber being consistently used in the home.
Sonny