At present there is no indication in the source tree that etc/zebradb/marc_defs/marc21/authorities/authority-zebra-indexdefs.xsl should be automatically generated from the authority-koha-indexdefs.xml file. There probably should be, so that developers know not to edit that file by hand (and know what authority-koha-indexdefs.xml is for).
Created attachment 3894 [details] [review] proposed patch
This patch can be confirmed by reading the code. Since there is no authority-zebra-indexdefs.xsl for UNIMARC, I'm marking this as Passed QA.
Pushed and merge to master
Seems to be working now. Closing.