Before I installed any mods, I've made backup of RTW folder. After that I had two bi/data/export_descr_unit.txt files - in my 'backup' BI-folder and in BI-folder which in RTW folder is (I call it current BI folder

).
Then I installed IJ-mod into RTW folder.
Then I installed Rio VII into RTW folder.
When I tried to do as you said (check and find 'armoured horse' mount), I've found out that:
1) In 'backup' bi/data/export_descr_unit.txt there are no any 'armoured horse' mounts
2) But 'current' bi/data/export_descr_unit.txt has 'armoured horse' mount
3) And rio/data/export_descr_unit.txt has no such mount
And I can't understand why 'current' bi/data/export_descr_unit.txt has 'armoured horse' mount. This file should have no 'armoured horse' mount.

It could become changed if I installed some mod into RTW-folder. Only IJ-mod I've installed there.
BTW. I still can't understand. Why this error does appear? Does Rio VII use current BI-folder files?