BIP44 defines the address gap limit to be 20. Which means during recovery, as when importing your master public key in a wallet for monitoring, the software looks 20 addresses ahead of the last used address.
If functioning normally, the software should only derive a new public address if the last one hasn't seen any transaction. You can't force the Ledger Nano app to create a new address. From BIP44 again:
Wallet software should warn when the user is trying to exceed the gap limit on an external chain by generating a new address.
This is to avoid the problem of having to potentially re-generate and scan an arbitrary number or public addresses.
So basically the recovery procedure is:
- Derivate 20 keys from the master public key
- Scan all adresses
- Take the last used one (child X) and generate keys up to X+20
- Scan the new addresses
- Rinse and repeat last 2 steps until nothing new shows up
There is a bit longer and general explanation of the system here.