what is the relation between reifiers and annotation blocks?

[lisp]

the syntax permits arbitrary sequences of reifiers and annotation block in an annotation.

[35] | annotation | ::= | (reifier | annotationBlock)*

what relation(s) among those elements and between them and the respective statements does a given sequence imply?

[gkellogg]

It's spelled out in the processing instructions with "curReifier". An explicit refier determines the identifier for a subsequent annotation block, unless it is followed by another reifier or end of triple. Without a preceding reifier, a new blank node is used.

[lisp]

why would on not make that apparent in the bnf by establishing a non-terminal to that effect?

this relation is a local syntactic construct which is better specified as non-terminal combinations than as an interpretation constraint.

[gkellogg]

I believe the grammar is appropriate, and the annotation production indicates that there can be an indefinite sequence of (reifier | annotationBlock)*.

Because of the state necessarily involved in parsing Turtle, the Term Constructors describe how the various productions affect the parser state.

If you have a better grammar that leaves less up to parser state management, suggest away. The combinatorics involved suggested this approach.