I have a similar problem.
Not sure if it was Lion or Mountain Lion that all day events have a default alarm of the day before. For me, with the birthdays calendar populating from Contacts, they still have the default alarm, but I spent all last year adding a second alarm for the day of the birthday (at 8am since that was the quick choice in ML), every time a birthday came up, and choosing to apply it to all future events.
Since installing Mavericks, all of those second alarms have been erased and the only ones that are in place are ones I've done for birthdays since installing (at 9am since that is the new quick choice) and some recurring appointments that are not all day events.
So now I have to spend the next year, or one big sitting, re-adding second alarms to all the birthdays. Frustrating.