Left deep grooves in the hard wood floors.These neighborhoods on the east side have been high crime areas for a long time, and might be better left to the professionals until the crime is driven out farther down MLK.

At least it's a unit you can live in while doing it a little at a time though.If you run short on money you could try using drywall mud to fill in the gaps/grooves in the paneling and then painting over it all.

Don't leave them there.I don't think you need to Tongue and Groove these.

The rotten wood brought melted snow and rain water along the grooves of the wood into the house where it created a nice waterfall in the hallway of the middle floor.  

When standard tongue-in-groove strip hardwood floors are put in place, they're first sealed and then finished.

I wouldn't re-plywood an entire floor with only one minor soft spot if I could access it from the basement, but if there was deflection everywhere I'd put down a good layer of tongue & groove OSB or plywood before I started with the flooring. 

I worked with a lady that had been flipping homes for a while that got into a groove with her teams and material suppliers that told me her way of going about it.

(Plus chemicals doesn't easy get behind an outlet face plate or down in a groove in the wood floors where they may hide)- I don't worry about it at all because it's outside of my control. 

Floorboards tend to be tongue and groove with a special profile on the bottom side to prevent warping.Good Luck!  

If you can do that in a pandemic, you're really going to be rolling once everything is moving and grooving again!!