Hey, pixies, I need some pedagogical advice!

Here's the deal. I am teaching an upper-level history course that meets Tuesdays & Thursdays, and the first midterm exam is next Tuesday. The course uses two books, one general text and one documents book.

Tuesday of this week, I reviewed the basic themes that would be covered, and told them they could bring the documents book to the exam, because I expect them to structure their answers around specific examples from the documents. One student asked how many questions there would be, and I responded that I wasn't sure if I'd give them two long essay questions or two medium questions and a shorter question, but that I would tell them something more concrete on Thursday (today). So it's an important detail that on Tuesday I promised them more information on Thursday.

Before today's class, I gave this more thought and decided that 1) they could use both books for the exam, and 2) I'd also let them bring in one page of notes. (I'm struggling to resist going off on a whole tangent about why I decided this, but it's not relevant to the main question here. Suffice it to say that much thought went into this question, and to be fair, I should have done more of that thinking a little earlier, but I'm pleased with the exam setup.)

So, at the beginning of today's class, I spent about ten minutes discussing the nature of the exam and the materials they'd be able to use, and answering questions about these. The students clearly understood the rules and were pleased with the setup as well.

And you can probably see this coming. Two students missed this class, and another two came in about ten minutes late, just after I'd finished this whole explanation. (My syllabus emphasizes coming to class on time, because I often make announcements and give quizzes and such in the first five or ten minutes.) One of the late students did come to me after class to ask what I had said about the exam, but the other did not.

What is my responsibility towards the absent and late students? It's been clear all along that this would be an essay exam, and nothing about the exam itself has changed, but I think it was also clear that I was debating about what kinds of materials to let them bring in. Since I clarified this only the class period before the exam, do I have an obligation to contact the other students to let them know? Or is it their own damn fault for skipping the class before the exam?

Here are the two options that are most tempting to me at the moment. I may post the exam information on the course website now, so that it's available to those who go look - on the premise that it would be wise on the part of those who missed class to check the website, but it's up to them. Or, I may post this information and email the missing students, but not until a day or two before the exam. I do NOT want to give the late/absent students the impression that I'll follow them around and make sure they don't miss any important information, but I also don't want to be unfair in any way in regard to an exam that's 15% of the course grade, and I particularly don't want to deal with students who show up at the exam and may throw fits that other students have the advantage of having brought in their notes.

The more I think about this, the more I'm leaning towards the first option, but I'd love any suggestions. What should be done, pixies, what should be done?