User blog comment:Icey The Yoshi/How do you guys get the birth dates on characters?/@comment-29952426-20160622001341

That's a good question. I think there are 2 characters who have birthdates taken from his videos:

Bowser Junior: Both 2014 and 2015 celebrated Bowser Junior's Birthday in late September (Even though Bowser Junior's Birthday Cake came out in June 2013)

Cody's birthday is definitely known to to be "February 29 2008" since it is clearly revealed. On any of the other characters i'm not so sure...