Vijay Kaul:
Although I have a great admiration for the graphic design and history of the Art and Craft of Heraldry, I have little knowledge and no skill. Please bear this in mind as you read my post.
I agree with you that, although the use of interlacing (plaiting, braiding) in Celtic Art is ancient, the introduction into Heraldry is modern. Examples of interlacing are found everywhere. For example, I have seen sketches of interlacing from Tut-Ankh-Amen's tomb (~1350 B.C.).
The most comprehensive book I have seen that discusses the methods of Celtic artwork is "Celtic Art" by George Bain, published around 1945. It may be found in a library. Modern books that I have glanced at seem mostly to be selections from Bain's book with "up-to-date" graphics.
George Bain would group Steven's work with "Celtic Interlacing Borders". He shows methods for constructing many interlacing borders. However, although he gives sources, he does not name the designs.
Your question and search for knots, names and symbolism is shared by most, if not all, members of the IGKT. Since the Celtic knotwork is not part of "traditional heraldry", it is not part of heraldry's descriptive language. Therefore, any names of knots, designs and symbolism will be modern speculation or invention.
To blazon Stevens' coat of arms, modern heraldry may have to coin descriptive names for the designs. May I suggest one for Stephen? Are you familiar with "The Ashley Book of Knots"? The knot tyer's Bible! The knot used by Steven is called "The Crossing Knot" - #1171 in Ashley's book. Virginia I. Harvey, in her book "Macrame" (1967, pg. 73) says " When cords are looped alternatively over each other, they are known as chains or, sometimes, bars. Two cords will make a single chain ...". Might I suggest the name: Single Crossing Knot Bar? Or, perhaps the Crossing Bar?
Please understand that the name was suggested with a smile and with a sense of humor!
I understand there is an official "College of Heraldry" in London, England. Have you considered asking for their advice and help? I am sure, if they don't know about your group, they will be thrilled to help others who are interested in heraldric design.
Please let us know if your search produces more information on your interesting questions.
Brian.