Having created a naming scheme set up to include CDTextTrackTitle in rendered clips and where the Preview section confirms this setup, the resulting exports leaves this field out.
“CDTextTrackTitle” can only be used in rendered titles, not clips.
A clip does not know what a title is (and a title could be made of several clips).
Hence you have to render titles, not clips.
The naming scheme dialog ignores the rendering context (eg. render clips vs titles), hence the previous is an approximation.
Ah, makes sense. Thank you!