Oh, dear! I am no help with a solution (wonder if they couldn't have been bleached), but just want to say that the floors look like they will be beautiful if they can be fixed. I feel your pain.

Sand it off and apply oxalic acid. You will need several treatments to even it out. Oxalic acid will not remove pet stains. Neutralize and remove all of bleach crystal before applying finish.

As per G ad S, but I'd consider a satin finish as well. Too shiny now! I'd also ask what you plan for trim, which isn't going to be great against the lighter floor.

If the goal is to lighten/brighten the house, it will take more than the floor stain to do that - It will involve the trim and the walls.

If the trim remains? The dark stain is far nicer, but with a satin finish. The trim makes the floor read quite orange in tone.

I have seen old Pine floors where the mismatch caused by being covered, would NOT sand out. A VERY talented finisher MIGHT be able to add tinted poly coats to the lighter areas until they match, then apply a final coat, but it's questionable whether the reward would be worth the effort.

Do you have pictures showing what the floors looked like BEFORE AND DURING refinishing?

The same thing happened in a flip house that we did, we just went with it and people absolutely loved the floors at the open house.

Your trim is beautiful and will still look wonderful with lighter floors.

IMO this is something that needed a better floor refinisher and a bigger money tree. This is ahuge job to get old pine floors refinished to look like new and all your trim will need stripping and redoing also. IMO better lighting and lighter walls colors with darkers floors would be my choice

It is unclear in your post. Did they STAIN the floor? In other words did they ADD colour? And when you say 'polyurethane' can we assume you mean OIL BASED polyurethane (the stuff that turns orange and smells horrendous for 30 days)?

Did the refinishers show you STAIN or COLOUR patches? Did they show you what your floors would look like with the finish APPLIED to the floor?

Please post photos of 'before' sanding, after sanding and then the colour swatches put down on the sanded floor that you picked from.

Scuff 'em up a bit and they'll be perfect.

Redo the floors. There are too many waves and dish-outs. Enough to cause sea sickness.

I think they're fine. It's an old house - you're not going to get "perfect, new" no matter what. Also, fwiw, those old pine floors were never meant to be exposed.

I like them even with the imperfections.

I think your floors and your trim are beautiful! Once you add back furniture, you won't see so many imperfections--and those that remain will add to the charm!

Thank you everyone. I guess what I imagined really threw me off. It is what it is.

Terrible sanding.
Look into Loba Invisible Protect.

I like the floors... this adds character in an older house. As with others, I'd have chosen a satin finish, but your furnishings will help a lot.