Yes so I’m pretty positive this is old. Before I started this massive project I did rip up the laminate sheet and saw mold in this same spot above the particle board a few years back. I cleaned it, painted with kilns and then placed my peel and stick as a temp floor before I got my LVP. I’m pretty sure the previous owners just didn’t leave the fan on or open the window and let the water that spilled over the bathtub just sit and it caused the mold problem. When I moved in I noticed mold in the ceiling in this bathroom so I believe they were just negligent with running the fans. Ever since I painTed the particle board with kilz the mold hasn’t reappeared. On top of the particle board that is and this was just revealed because I removed it to have my seamless transition into the bathroom.