My first house was built in the 1930s. The guy I bought it from was an electrician. He was also a fucking hack. He replaced "all" of the original K&T wiring with romex and upgraded the panel from a 60A fuse panel to a 200A breaker panel. He did all of this work poorly, and very little of it was done to code.

All 2nd floor lighting circuits were still K&T. There were running splices in the basement and the attic. The main wire from the pole to the meter was replaced when the new panel was installed, but the penetration in the side of the house was never sealed, which meant that water collected in the bottom of the panel whenever it rained.

Over the course of 10 years, I spent countless hours discovering and repairing the previous owner's hack work.