What does "to all 3rd parties" mean? It doesn't sound like it means "people you distributed the derivative work to" which is what I previously understood.
Let me quote 2b again:
b) You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License.
This means that the _license_ is valid for everyone else. It doesn't mean that you must give (or make available) a copy to anyone else.
But if you distribute your program or derived work to company A and later find company B has a copy, you can't say "no, I didn't give permission to company B.
This ressurects cases of embedded linux routers without source; who must supply the source to the end customer?
The one who gave the binary to the customer (this is the distributing company, not the shop clerk, usually). It's their problem if they didn't get the source with their binary, not the user's.
/alessandro
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PS: please avoid sending two copies of your mail message. The html is definitely unneeded and often exceedingly long. You should configure your mailer to only send the text version of your messages.