Can you please tell me what the general rule is. Once you have sent out Birthday invitations for February, ie. beginning of December and people have said they are coming, do you still check just before the event, so you have catering numbers?
I'd have thought, if you want to be confident in the figures you have then you check, but if confident folk would have informed you if their plans change, then you wouldn't. Your choice.
If you really want to know, i would just send each person a message asking a question or saying that you can't wait to see them. That should act as a reminder while also prompting people that can't make it to let you know