Guarantee that all "nonfree open source" is different readings. Take the NASA case. If youu read it as strictly as Stallman does then it violates the OSD also. The people at OSI at the time it was submitted read it more like a lawyer and decided it was compliant. Possibly today's OSI would disagree. Possibly tomorrow's FSF would agree. It's not a difference between free software and open source but a difference between how two sets of humans interpreted the text of the license.
Eh, OSD 3 just says that derived works must be possible, it doesn't say that you must be able to incorporate third party source code into the derived work. Meanwhile the FSF's definition explicitly calls out this freedom as an essential component of Freedom 1:
> One important way to modify a program is by merging in available free subroutines and modules. If the program's license says that you cannot merge in a suitably licensed existing module—for instance, if it requires you to be the copyright holder of any code you add—then the license is too restrictive to qualify as free.
