The author might have a higher chance of figuring it out. This is playing the likelihood game though. In perfect world, the code would be tight and small enough

The author might have a higher chance of figuring it out. This is playing the likelihood game though. In perfect world, the code would be tight and small enough that you wouldn't take long to understand it, and then the complex components (there are always a bunch of these) are well tested and documented. Especially rationale for design decisions or implementation quirks. Old code does not necessarily mean legacy code.