There better be a way to use at least two normal maps on a single texture, i believe it's a thing that works with map brushes because they use the 'LightmappedGeneric' shader that allows multiples of certain things, but VertexLitGeneric currently only supports one normal map per texture
Which sucks because games for years now have had the usual normal map you see at any distance, but then there would be the detail normal map for when you view models up close