It's very clear cut, actually...
Posted Jun 1, 2011 7:12 UTC (Wed) by khim
In reply to: How much GNU is there in GNU/Linux?
Parent article: How much GNU is there in GNU/Linux?
When you contribute to GNU you assign your copyright to FSF. As long as you do that yes, it's GNU contribution. Is it voluntary or not is good question, but it's clearly part of GNU.
If the supposed fork will stop assigning copyrights to FSF you can claim it's no longer GNU project (like happened with XEmacs). The history shows it's not easy to maintain viable full-blown fork of GNU software (it's possible to maintain set of incremental patches like EGLibC does - but this hardly can be called a separate forked project).
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