With periodic input from SK, I've finished writing the XSLT to transform the existing XML to something much closer to what the editors want to produce: multiple instances of many tags are collapsed into one, and bibl references copied in multiple places. The problem now is that oXygen 11.2 seems to have serious issues running a transformation scenario on the files; it runs out of memory (I've already upped its memory allotment twice), or it simply stops after one file instead of running through all the selected files. In the end I gave up on it, and ran the transformations in oXygen 10.3, which has no problems.