How can I fix dark floor stain absorption without starting over?
It really is going to be next to impossible to match up those various areas where you have tried the sanding and re-sanding. My recommendation, if the flooring material still has enough depth to the tongue and groove to permit more sanding, is to re-sand the whole floor uniformly. That may be best done by using a drum sander so as to get as even of surface as possible. Do be aware that operating one of those is tricky and in inexperienced hands can ruin a good floor very quickly.

Once you have cleaned the floor of all the sanding dust you should look into sanding sealer products that you can apply to the surface. These are designed to allow stain to be applied more evenly than just putting stain on raw open grain wood.