Well, then they are one in four. The other three were quality, performance and correctness. Simply re-implementing something, or writing something that is poor software isn't sufficient.
As for knowledge: yes, it is more valuable than the software. That does not imply the software is the only place where software is stored. In its most useful form it is stored in people. Which is why you should revisit, and rewrite, code that is important often enough to ensure the knowledge is passed on.
However, don't forget to make room for new knowledge and new ideas. That has hardly happened to Office suites for 30 years. They just tend to become "more".
As for knowledge: yes, it is more valuable than the software. That does not imply the software is the only place where software is stored. In its most useful form it is stored in people. Which is why you should revisit, and rewrite, code that is important often enough to ensure the knowledge is passed on.
However, don't forget to make room for new knowledge and new ideas. That has hardly happened to Office suites for 30 years. They just tend to become "more".