In AACR2 there is the following rule:
2.5B11: "If numbered pages or leaves are printed on a double leaf (e.g., books in the traditional oriental format), give them as pages or leaves according to their numbering. If they are unnumbered, count each double leaf as two pages."
I discussed with a rare book librarian today and have the following suggestions:
1) In "traditional Chinese formats" or "traditional oriental formats" (all ancient books in East Asia are similar in format), thread-binding is the most popular format. There are also many other formats, but they account for just a small percentage. I suggest that "the traditional oriental format" be changed into "some traditional oriental formats" in RDA.
2) For thread-binding format, page numbers are usually printed in the middle of the folded leaves and appear at the margins of book pages. Therefore, we can just describe the leaf numbers, not the page numbers -- in fact, there are no page numbers. In late Qing dynasty (in pre-modern history), some thread-bound books have pages, but they are not representative.
In modern rare book cataloging practices, we usually do not describe page (or leaf) numbers in the physical description area. We just describe volumes, parts and boxes in the physical description area. The reasons are:
a) It is the traditional cataloging practice.
b) There are various paginations in a single title of traditional binding format.
In the drafting of RDA as the revision of AACR2, practices in various countries should be considered.