Despite the rumors, theological development of the Trinity hasn't ceased. Progress continues. In the 20th century, the work of Van Til helped to highlight the need to have further development to counter the attacks from liberals.
Liberals and other heretics often raise good questions. Answering heresies is how theological development progresses. We have the comments of the incarnation in 1 John because of the docetists. We have the early creeds due to Christological hereies. Van Til responded to 19th century German idealism.
The Function of Perichoresis and The Divine Incomprehensibility (Lane Tipton)
The Triune Personal God Trinitarian Theology In The Thought of Cornelius Van Til (Lane Tipton)
> Critical text! This is the standard!
This work truly explains the Trinitarian development of Van Til.
Introduction to Systematic Theology (Cornelius Van Til, ed. William Edgar)
> Be sure to get the annotated edition
The Trinity and the Vindication of Christian Paradox:An Interpretation and Refinement of the Theological Apologetic of Cornelius Van Til (B. A. Bosserman)
The Eternal Generation of the Son: Maintaining Orthodoxy in Trinitarian Theology (Kevin Giles)
This is an important book. It helps to clarify the relationships within the Trinity. You can find quotes from this book on this website: Quotes