It sounds like you’re just reading code with zero context and no further information about the design, all the mistakes along the way and the code that didn’t m

It sounds like you’re just reading code with zero context and no further information about the design, all the mistakes along the way and the code that didn’t make it. My first recommendation for large changes would be pair programming (there’s plenty of screen sharing tools out there) or at the very least having the developer take you through the code.