Difference in TSS between Desktop App and Calendar for same workout

Today I’ve noticed for the first time that the TSS for a workout differs between the desktop app and the completed workout in the Calendar. The workout was bluebell and in the app the workout summary say 85/76 TSS which is a bit strange as I only completed the prescribed workout and extended the workout by 2min for the cool down so wouldn’t expect a large difference in TSS. The trainer also dropped out for the last interval.
In the Calendar TSS is 75/76. Has anyone else noticed this before? And which TSS is correct?