My french drains were incorrectly installed and I had water sitting around my basement for 3 months. I had a large mold bloom in the unfinished part of the basement and mold grow on the baseboards. The moisture levels in the baseboard ranged from 21 to 24. One wall was moisture tested with a probe and the drywall removed to 1 foot (levels were 17). The rest of the room was not probe tested. Room has been dried out with 4 dehumidifiers for a week. The re-mediators say there is no need to replace the drywall even if it was wet. Is this accurate? They have also not checked behind the drywall for more mold as non was visible on the front side.
They are wrong. Drywall is gypsum and paper. In the presence of standing water, paper will grow mold and gypsum will turn to mush. It is water-soluble. That means it will dissolve. Give it a kick with your shoe on. It will probably feel soft and mushy.
Replace everything with materials that are not affected by water: cinderblocks, cementboard, lime plaster, tile, etc. Wood and drywall in a basement are, in my opinion, terrible ideas. Basements flood. It's just a fact of life. And when they do, all the pretty wood and nice drywalled stud walls are toast.