Having an open, reusable system, usually delivered with complete source code, is not the whole story to universality. Unix is the most significant example of this situation: when its source code became available, discrepancies appeared between various patches very quickly.
Probably as a consequence of this situation, other source-code distribution organizations have set up a consistent validation procedure to integrate patches and versions into the so-called "standard" product (Free Software Foundation).
YAFL's approach to this problem is based on inheritance: patches are not meant to happen through modifications to the original source code, but through the definition of new compilers, which define ad hoc classes to inherit from existing compiler classes, and change their behaviour by redefining one or more methods. These new compilers can be built without altering the existing code in any way.
Since the original code is left as is, no matter how esoteric the newly defined compilers are, the kernel of the compiler can be upgraded, without losing the modifications and enhancements which have been applied.