I've answered my own question and learned a few things along the way:
1) The Issue Manager text fields are NOT linked to the record with the project (P_) and sheet (S_) text fields. In other words, do not replicate the online manual instructions of selecting a text string intended to be manipulated with the IM and linking it to a text record like you do with the (P_) and (S_) fields. Instead, using the text tool place a text "box" in the custom title block and actually type the term ":iNote" in the text box itself. Do not attempt to link this text "box" to any record. The online instruction manual did not make this differentiation clear.
2) In building my custom title block, I grouped various items (including text fields) together for easy re-arrangement while designing the custom title block. The text fields linked to either a text record or to the Issue Manager failed when nested in a group. The ":iNote" field worked when grouped but the text typed in the IM laid right over the top of the text ":iNote" - so it looked like I had two text "boxes" with no fill on top of each other. I ungrouped everything and the links worked fine.
3) When building a custom title block, make sure that all text fields are EXACTLY the way you want them to look BEFORE linking them to a text record. After they are linked, any change to the text formatting (bold, etc.) does not seem to take effect in the title block symbol. To make changes to the text formatting after the text field had been linked, I had to completely delete the text "box" in question, recreate it with the revised formatting, and then re-link it to the text record.
Lessons learned.