FWIW
jwfacts: Watchtower 15/10/15 p.3 states that helpers are of the
Great Crowd. "Since 1992, the Governing Body has appointed experienced,
mature Christian elders to help its committees carry out their work.*
These helpers, from among the "other sheep," provide valuable support to
the Governing Body."
That WT above, does NOT list Cook as a helper.
I don't believe that it is rigid that the GB helpers are specifically 'other sheep' and NOT 'annointed' - I suspect that the 2015 article was written the way it was because, at that time, all the helpers where, coincidently, 'other sheep'.
When the GB helper came in to being, the WT repeatedly highlighted that:
Watchtower April 15, 1992 - Announcement: Assistance for Governing Body Committees
Therefore it has been decided to invite several helpers, mainly from among the great crowd, to share in the meetings of each of the Governing Body Committees, that is, the Personnel, Publishing, Service, Teaching, and Writing Committees. Thus, the number attending the meetings of each of these committees will be increased to seven or eight. Under the direction of the Governing Body committee members, these assistants will take part in discussions and will carry out various assignments given them by the committee. This new arrangement goes into effect May 1, 1992.