Priority of cleaning up unclear legal status

1) Add an explicit link to http://www.apache.org/licenses/cla-corporate.txt and the revision number in the preamble, just to avoid any potential doubts about whether "a Software Grant and Corporate Contributor License Agreement ("SGA ")" refers to the standard Apache one or a different one negotiated by IBM and the Foundation (in much the same way as "released under the terms of the GNU GPL" is ambiguous as to which version it refers to).

2) Add "These materials are contributed under the SGA" to point (2)

I think that those would make the intended copyright status completely unambiguous, but I think the change you've already made goes a long way.