gmbs In the letter Wignall refers to Elastix MT.
Issabel is forking Elastix 2.5 and 4 (not MT).
So that section does not apply. Elastix 2.x and 4.x includes a freePBX rpm package, that as far as I can tell, has no modifications to the original code. So I think that all copyright notices are retained (but I could be wrong, a proper code audit should be performed). Wignall only concern for Elastix 4 is that is an outdated FreePBX (not the latest available).