Thanks for your contribution to the thread! More below.
The OFL doesn't refuse to admit that font sources exist - rather the
contrary - it acknowledges the fact that beyond the binary font files
themselves, which you can already do something with, there are a lot of
different elements which can be used as extended font sources. It avoids
the problematic question of defining precise source requirements for
the "preferred form of modification" when there are various ways of
modifying and building a font: "preferred" for who exactly? A very
strict source requirement would alienate the vast majority of designers
we want to see joining our community!
So the OFL model intentionally doesn't place strict requirements on
releasing these extended sources needed for a full build but at the same
time it *makes it possible and strongly encourages* (via the FAQ) the
author choosing this model to release everything that can be useful to
designers: data files, glyph databases, smart code, build scripts,
documentation and rendering samples.