Something belated comes after the fact. If you are late to deliver a birthday greeting, then make it a "happy belated birthday" card.
Belated Christmas gifts come after December 25. Belated birthday greetings are still sweet, but a belated New Year's Eve party? Sort of pointless. Belated can refer to less effective actions when used in more significant settings — consider "a belated push to secure tax breaks for the working poor" or "a belated apology for indiscretions committed during the senator's scandalous college years."
