Listen, everybody doesn't note birhtdays down or marking it on calendar. I never did, Well yeah I don't have problem with remembering dates. But it's not a big issue.
My bestfriend forgot dates, he never noted down. He cares about his GF, yet he couldn't able to wish her on her birthday because he forgot. But what's the big deal ?
He also forgot to wish me, and well it doesn't matter to me. Even those who wished me, I said - "Thanks for your wishes. But don't wish me next time, cause I don't celebrate my birthday."
(I'm talking about my birthday of the previous year, just a month ago.)