I made a little script to display the areas covered by each XML file:
https://github.com/Juanvvc/plot_regions Images are not updated to the last version of FGDATA, but to the version available some moths ago. I'm not aware of major changes lately in regions.
azores.xml is only applied on the Azores islands:
azores.xml only defines a region in the middle of the Atlantic:
https://sourceforge.net/p/flightgear/fg ... azores.xmlI believe the message you saw must be something else.
Also, there are images showing which regions define a material. For Rock (the areas are drawn according to their priority)