Looking at the example in the specs one would assume the scoring software should render the text as defined in rehearsal element text.
Dorico does not do that, but instead overwrites the value by its own sequencing algorithm. Worse: if one uses suffix in a rehearsal mark in Dorico, exports that to musicXml and imports back to Dorico, the suffix is lost.
The root cause is lack of custom, non-generated rehearsal marks, which Dorico enforces even on musicxml import.