What you described above is not how CGC Signature Series works let alone how CGC witnesses work. First of all, CGC Signature Series doesn't have to be at every con for a book to qualify for the yellow label / Signature Series. That's why they have a network of approved CGC Signature Series facilitators that work various cons / private signings. A facilitator, however, can't witness the signatures themselves - that's the role and literal job of the approved CGC witness. A facilitator has to have an approved CGC witness work with them per event. A CGC witness just doesn't get approved to witness an event without working with a facilitator or CGC themselves (if they are at the event). If the Eastman books were signed privately away from the crowd, that's fine as long as the approved CGC witness was present for the signing and that there was an approved CGC Signature Series facilitator working that event. That scenario isn't uncommon. But if CGC's Signature Series process wasn't followed for the book you posted, then CGC Signature Series needs to investigate what happened.
For my $.02, I don't feel any signatures outside of CGC Signature Series should get the yellow label. In their posting, CGC specifically distinguished the difference between JSA authentication and CGC Signature Series - in other words, they made a point to remind everyone which one is witnessed directly and which one is not. One shouldn't have to look at the fine print on a yellow label to figure out if it was JSA authentication or not. The book's label color itself should tell you right off the bat what the book is all about. In my humble opinion, adding JSA authentication to the yellow label series at minimum dilutes the integrity of the yellow label. JSA authentication should get its own label color.