> i heard, and then read,  that GPL patches CAN be run in closed source systems running libpd, etc.

it's just GPL externals that you can't use without sharing the code. 

Whether this is true or not, I think it's largely irrelevant.

If company X is a reputable company selling proprietary software, their lawyers will consider

anything licensed "GPL" toxic and avoid it like the plague.

If company X is a disreputable company, they're just going to bundle whatever they want

regardless of what the license is. See all those cheapo IoT devices that ship patched versions

of Linux without releasing their changes to the Linux source.

There _might_ be some edge case where a naive but otherwise good-faith developer wants to

sell proprietary X and tries to "roll their own" interpretation of the GPL to suit their distribution

case. But applying engineering principles to a legal document will almost always get you whatever

it is you're looking for, so I'm not sure the license text actually matters that much in such an

edge case.

-Jonathan