Just got an email from AY notifying my flight AY61 HEL-HKG on 3.10 has been cancelled. The schedule for AY61 was dep 17:10 arr 8:10.
The replacement flight in MMB is AY99 dep 17:25 arr 8:10.
Think this confirms the AY99/100 is a replacement for the AY61/62, not an additional service.