That sounds about right to me. The (in)famous Filioque clause was added in the West to combat a specific heresy which was not prevalent in the East. A local addition, it was gradually adopted by the whole western Church until at some point it was accepted universally. The East, not encountering the same issues, just didn't see the point, or the need to alter the form of the Creed which had been decided by that time. And the Eastern churches have never liked agreeing to anything without full consultation
. They just never saw the need for the clarification.