I briefly helped with some mainframe/legacy modernization work. Their hard part was determining which feeds and datasets were still needed by someone, somewher

I briefly helped with some mainframe/legacy modernization work. Their hard part was determining which feeds and datasets were still needed by someone, somewhere. Over the decades, 100s were created as needed (ad hoc). No inventory. No tooling (monitoring, logging) to help. It's likely only a handful were still needed, but no telling which handful. The bosses were extremely risk adverse. eg "We can't turn that off, someone might be using it." I suggested slowly throttling all the unclaimed (unknown) stuff over time. Wouldn't break anything outright. But eventually someone would squeal once they noticed their stuff started lagging. Then incrementally turn things off. See if anyone notices. Then outright remove it. Nope. No can do. Too risky.