I use the equals sign for two basic purposes: to depict apposition and, much less frequently, pleonasm. I think the equals sign should always be used for apposition. In your handwritten diagram, the symbol you are using instead of the equals sign would indicate that the word with that symbol is a modifier or qualifier of the word with which it is associated but is not the same person or thing as that which it modifies or qualifies. An appositive, on the other hand, doesn't modify or qualify the word with which it is associated, but is the same person or thing as that word, and "piggy-backs" on that word in order to bring clarification to it. Apposition isn't really a syntactical category at all, since the appositive refers to the same person or thing as the word with which it is in apposition and has the same syntactical relation to the rest of the clause. The appositive simply clarifies the first substantive. If you were to take away one or the other, the sentence or clause would still make perfect syntactical sense, since both words refer to the same person or thing, are in the same case, and have the same syntactical relation to the rest of the clause.
I think you mentioned before that you have Wallace's grammar. He has sections on simple apposition for each of the cases, and I think you may find them interesting. For the nominative, pp. 48-49; for the vocative, pp. 70-71; for the genitive, pp. 94-100; for the dative, pp. 152-153; for the accusative, pp. 198-199. For the genitive he has two sections and contrasts the genitive in simple apposition with the genitive of apposition, so the treatment of the genitive is longer and more involved.
Keep up the good work! It's great to hear that you are enjoying the diagrams and even better that you are diagramming yourself.
Hope this helps,
Edited by Steve Lo Vullo, 26 December 2016 - 07:37 PM.