Read a thing once from some old house forum about how bathrooms in places from that era were basically built to fail, no vapor barrier, tubs set right against the studs, water just sits there for decades. Guy was saying the mold is always there, you just don't know it until you open things up. Made me think about my own place, every wall I open now is a coin flip. That gap trick is smart too, lets the wood breathe instead of trapping every bit of steam back there. I started taking pics of every wall before I close it up, just so I know what's hiding if something comes back. Wild how one bad demo changes how you look at the whole house.