@vathpela @glyph I find in the text of GPL2: "You may not impose any further restrictions on the recipients' exercise of the rights granted herein."
If Sony [or whoever else] made someone sign an NDA saying they could not distribute the GPLed software they gave them, Sony was violating the GPL, and therefore did not have the right to distribute the modified GPLed code in question.
@vathpela @glyph (The GPL3 has a more complex clause. The fact I find the GPL3 harder to interpret as a non-lawyer is a reason I prefer GPL2.)