Just to update that previously for the first year of the card my quarter dates are always consistent, eg 8/2 - 7/5, 8/5 - 7/8...

After calling in to check on the latest rebate not being credited, the CS informed me that my quarter dates has been moved to the 12th and this is due to +1 day every quarter, and it seems to be in-line with the latest updates posted on this thread.