VoiceOver misreads days of the week

Despite having the days of the week abbreviated on screen, VO will read some of the days in full in this manner:

• "Sun" - read as Sun
• "Mon" - read as Mon 
• "Tue" - read as Tuesday
• "Wed" - read as Wed
• "Thu" - read as Thursday
• "Fri" - read as Friday
• "Sat" - read as Sat

Is there any way I could programmatically set VO to read the values consistently?