I have received it twice if I remember it correctly.
The first bonus was based on my real birthday because at that time my VIP host asked me about my birthday.
The second bonus was based on my account's date creation (the new birthday bonus system) where users get a special symbol in their username as can be seen in chat or in our own profile.
VIP host sent me the bonus directly to my vault balance IIRC for the birthday bonus, but if users has no VIP yet then I guess they get the bonus from live support.
Is there really any bonus for account birthday? My Stake account was created more than 4 years ago. But I have never received any bonus on my account creation date. I haven't submitted any kind of personal details to my Stake & Primedice account. I have VIP host on Primedice, but she never asked me to know my birthday date. I'm platinum two at Stake without any VIP host. Perhaps, the birthday bonus isn't available for unverified users.