The OP asked for horror stories. I didn’t mean to imply rewrites can’t work, only that I’ve never seen it work (in 40 years programming). My very first program

The OP asked for horror stories. I didn’t mean to imply rewrites can’t work, only that I’ve never seen it work (in 40 years programming). My very first programming job at Nike was what was then called a “conversion,” moving a working code base from one platform (PDP-11) to another (DECSystem 20). Conversions were common rewrite-type projects back then (‘70s) because every vendor and computer model had a unique OS and set of languages and tools. That project succeeded. Throughout the project the project manager (one of the best I’ve worked with) resisted every attempt to expand scope so we could focus on getting the current functionality working on the DEC 20. It was partly automated and then required line-by-line examination of the source code and rigorous unit testing. I wouldn’t call it a ground-up rewrite, no new features got added and we had a working system to start with. It was more like an evolution. I worked on other conversions early in my career and they mostly got derailed when management and users took the opportunity to “enhance” what was working as part of the straight conversion, and/or when the programmers were allowed to get carried away adding functionality themselves.