I see a lot about source codes being leaked and I’m wondering how it that you could make something like an exact replica of Super Mario Bros without the source code or how you can’t take the finished product and run it back through the compilation software?
It highly depends on the programming language used and how much debug information is left in the build. Production builds of software usually have debug symbols and other information useful during development stripped out to save space and improve runtime performance. Even when it is technically possible to decompile built code, the decompiled result may not be human-readable to the point of being useful. Imagine reading source code that has random names for variables, functions, modules, etc, or code that does not have any discernable organization.