Other early works

[SmithSamuelM]

A couple of other early papers that you might want to reference. Although they did not use exactly the term Self-Sovereign Identity they did use the term Sovereign with regards identity.

The first one dated 2016/01/19 Soverign-Source Identity, Autonomy, and Learning by Phil Windley

The second one dated 2106/03/29 Identity System Essentials by Samuel Smith and Dmitry Khovratovich has a section on Sovereignty in identity systems including control over identifiers and the identity graph.

[SmithSamuelM]

http://www.windley.com/archives/2016/01/soverign-source_identity_autonomy_and_learning.shtml
https://github.com/SmithSamuelM/Papers/blob/master/whitepapers/Identity-System-Essentials.pdf