@Another C10 here is reference from horses mouth as it were:
Excerpt from NEMA publication on flooding and water damage: (I highlighted part on nm-b romex, it seems to indicate an issue if that paper become wet. Also included link to NEMA paper)
Wire, Cable, and Flexible Cords
When any wire or cable product is exposed to water, any metallic component (such as the conductor, metallic shield, or armor) is subject to corrosion that can damage the component itself and/or cause termination failures. If water remains in medium voltage cable, it could accelerate insulation deterioration, causing premature failure. Wire and cable that is listed for only dry locations may become a shock hazard, when energized, after being exposed to water. The following recommended actions are based upon the concept that the water contains no high concentrations of chemicals, oils, etc. If it is suspected that the water has unusual contaminants, such as may be found in some flood water, the manufacturer should be consulted before any decision is made to continue using any wire or cable products.
Items Requiring Complete Replacement:
Any wire or cable that is listed for dry locations only, such as type NM-B cable, should be replaced if it has been exposed to water. Any cable that contains fillers, such as polypropylene, paper, etc., should be replaced if the ends of the product have been exposed to water.
Section continues with info related to THHN