You could enforce it like that - i.e. require all cards to have titles.

But I don't think you NEED to.

I would assume that the way you know the order of the cards, is that you have some unique ID on the flow of the cards, no?

E.g. You know that A is first, then A.1, then A.2, then B.

So all you do is when you are exporting to PDF, you put the sections/cards in that order.

I think that should suffice, or am I missing something?