The un-announced nodes/channels are linked to your direct peers (LSP or other public nodes) you have channels. But only your peers knows about the route towards your private node.

The private nodes also are storing a local copy of the LN graph so next time when you send a payment, it will "know" more or less a route towards another private node.

That's why if you run a private node, have at least one channel with a public node. You can have any number of direct private channels to transact with direct peers, but if you want to go out to any node available in LN, you must have at least one route through a public node that can reach more public and private nodes.