okay, as far as I can see you save two things with this command:
- the private key (1 slot)
- the public key (1 slot)
Therefore you can only save 16 keypairs, but 32 keys. You can see every slot stored with the command
It’s a bit like the three keys on a OpenPGP Cards. Technically you can store 3 keys, but they normally belong to one identity as GnuPG expects two subkeys - one for authentication and one for decryption only.
So it is a bit tricky to keep track here, what the number of keys means for the own use case. One may only saves some rsa keys (or certs) without corresponding pub key or alike, but most will probably save privkey and cert or priv and pub key.
I dunno if you can just remove the pub key (and save it elsewhere), to be honest. Maybe someone else here does.