I thought that face orientation depends on face index, but my last test showed that I was wrong. Here you can see a mesh with 0 faces, extrudes by GN (regular Extrude acts similarly, GN is used for demonstration purposes):
Then I mirror a set of edges, it starts to extrude with different face orientation, but when I reorder indexes, it has no effect. But how does Blender keep that information in a set of edges then?
Moreover, direction is saved even if I connect edge loop with other:
Vertices have normals, but they have no effect also: