Old Baseboard

I removed baseboards in a few rooms where I had done work and the drywall was removed to the top of the baseboards. Also, can I caulk or use expanding foam to seal up any gaps between the floor and wall behind the baseboards? Do I need to repair that before putting the baseboards on. Im the one that brutalizes drywall behind baseboards.

The sheetrockers always do a terrible job down by the floor with a big curtain of mud that holds the baseboards uneven and out of plumb. I'm replacing the baseboards before the wood floors are refinished.

The baseboards will cover it up.

So I go through and chip and smash all that stuff out of there first and I'm not even sorry. You should probably fill with a small piece of wallboard or wood to bring it out flush.