That's the thing. The spad has the following:
[Decal016]
MeshName=Fuselage P
DecalLevel=1
DecalFacing=LEFT
FilenameFormat=Sq
Position=-2.19,-0.03
Scale=1.50
DecalMaxLOD=3
The 'Sq' is, I presume, the squadron marking, the definition of which comes from the loadout dropdown. . If I do the same to the Nieuport 17 generic decal.ini, and chose, say, "Esc 3 cigognes" from the loadout list, I get something, but not the stork I want. There must be something, somewhere, that links the list given in the loadout dropdown (which as near as I can tell comes from squadronlist.ini) and the correct insignia.
Now, apparently the squadronlist.ini is the link what connects the insignia tga with the correct squadron. For example, Nie.3 'Les Cigognes' is squadron 26, and sq026 is the correct insignia. But it doesn't work right. I change the decal entry in the Nie.17 file thusly:
[Decal001]
MeshName=Fuselage
DecalLevel=2
DecalFacing=RIGHT
FilenameFormat=sq
Position=-1.7,-0.35
Scale=0.65
DecalMaxLOD=3
Still looking.
And the select the 3rd Cigognes, I get the 13th Aero Squadron, coincidentally, the 3rd entry in squadron.ini.