Do you mean they may be hidden templates?
No, that's not what it means.
Sometimes, EA doesn't bother to give us the SC4 files for various neighborhoods. Sometimes, they ship an SC4 which doesn't actually match the neighborhood. The correct SC4 files are not hidden, they're
missing.
I seem to remember that it's possible to extract the terrain itself from your TS2 neighborhood and import it into an SC4 city, but I don't know of any way to extract the roads or neighborhood decorations.
Alternatively, there are ways to extract the terrain from one TS2 neighborhood, including roads and neighborhood decorations, and create a new TS2 neighborhood.
If you're interested, I can try to find you a link.