There was plenty of prep for comps, although I think maybe you're using the term narrowly. And maybe all you're referring to is "from the faculty," in which case that's correct, although (see below) because written comps were a new thing, I don't doubt that students would have asked professors how it was all going to work -- that sort of thing.
The one-sentence description of why the students were nervous and uncertain was that it was the first time that (a) the exam was on the same date for everybody and (b) it was written. Both were completely new to faculty and students.
At Harvard, before written comps arrived, you had 2 years of classwork, and then were expected to take as long as you needed to prepare for your first set of orals, which you then scheduled when you thought you were ready. There was no defined time of year for orals, but it was common for students to schedule them in the spring of the year following the year they completed their course work.
We had two sets -- the "generals," during which 5 professors grilled you for a couple of hours about anything to do with anthropology as a field -- and then the "specials," which were narrowly about your intended (or sometimes completed) fieldwork. Some time usually elapsed between generals and specials. I think the Department would have been displeased by a student who took much longer than an academic year (after having done the coursework) to prep, but there was no regulation about it that I can remember.
The 1969 comps were the first written ones and the first ones taken by all the appropriate grad students at the same time. But the ethos and collective student experience in the department was with orals. People always talked about their orals, in general, so you always knew the kind of thing you'd be facing in that room. So the older students could be helpful to the younger ones.
When we were getting ready for generals, we didn't so much study together as we practiced together. We would sometimes meet and students would play the roles of questioners. This was important and useful because in orals, obviously, you're sitting there and must immediately answer the question.
But no one really knew what the written comps would be like. I think (but can't remember for sure) that they were told something about the way the exam would be organized -- in other words, the sections they might expect, how long they'd be given to write their answers, if there would be any choice of questions, and so on. I didn't pay attention, because I'd already completed my generals and was headed for the field.
For the first written comps, as I've said, there was a lot of uncertainty. In all the following years, there wouldn't have been so much. I don't remember being told about study groups, but I wouldn't be surprised if there had been some.
I believe that the professors (and probably the instructors/lecturers) submitted questions to some central committee, which put together the actual exam. More details than that, I don't have.
