That'd be me sometimes lol. I have this folder of reminder notes, and when I learn of a friend's bday I just add it, and even if we don't talk, I'll send a message to wish them a happy bday, each year, unless I can't contact them, or it turns out they were complete assholes. (The latter hasn't occurred so far, nobody so bad I wouldn't wish them a happy bday, thankfully...)  
It's surprised some people that I remember, (and continue to/that I bother) and made their day once or twice, so that's good enough for me. :)