Vent: Chasing a leak in the old Montgomery Ward food court

Got a call about moisture damage behind a drywall panel in a dead mall near Akron last Tuesday. The place closed in 2019, but the roof still drains into a shared line. Tore out the panel and found a copper line that had been punctured by an old anchor bolt, probably from when they hung a sign back in the 90s. Water had been seeping for months, rotting the framing behind a pretzel stand. My crew spent two full days rerouting it because the original path ran under a sealed concrete slab. Cost the property owner about $3,400. What got me was the mall manager saying they'd noticed a musty smell since spring but figured it was just the building. Has anyone else found water damage that could've been caught way earlier if someone checked early signs? What did you do about it?