Why are changes that I made to the Result Format not appearing in Markbook?
You most likely haven't 'Validated' the Result Format.
This is achieved using TASS.web Academic Reporting > Setup Information > Assessment Setup on the 'Result Formats' tab.
Select your Report Type.
Click 'GO'.
Click 'Validate' at the top of the screen.
Check that you have made the changes to the correct Report Type linked to the Reporting Period that you are viewing in Markbook.
The Report Type is linked to the Reporting Period (Year and Semester) in TASS.web Academic Reporting > Setup Information > Assessment Setup on the 'Result Periods' tab.