A reasonable request still needs to arrive before the moment of disappointment.

Timing changes what a request is. Asked beforehand, it is information the other person can act on; asked afterward, the same words are a complaint, and they arrive with an implication that someone should have known. It is simply that a request made after the fact cannot be granted, only regretted.

Before the birthday, the visit, the deadline, say the thing you would otherwise be disappointed about. Keep it short and free of justification, since a simple preference does not need a case. And if you have missed the window, say it as a note for next time rather than a grievance.