Restoring password using unencrypted and encrypted wallet

[x-creature]

Hi guys,

I have two copies of my wallet: unencrypted and encrypted. All keys from unencrypted wallet are also in encrypted version. I can access half of the private keys (on the picture: key 1, key 2, key 3).
Second wallet is encrypted and have more keys (key 4, key 5, key 6).

 wallet unencrypted        wallet encrypted
+-------------------+    +-----------------+
| key 1 unencrypted |    | key 1 encrypted |
| key 2 unencrypted |    | key 2 encrypted |
| key 3 unencrypted |    | key 3 encrypted |
+-------------------+    | key 4 encrypted |
                         | key 5 encrypted |
                         | key 6 encrypted |
                         +-----------------+

Base on unencrypted wallet, is it possible to restore password for encrypted wallet?
If not, is it somehow easier to brute force password in my situation?

[RGBKey]

Unfortunately not. It is not any easier to derive a password from an encrypted and unencrypted version of a file than it is to find the unencrypted version of an encrypted file. Also, since the files aren't even the same file (one includes more private keys) it wouldn't be possible anyways.

What wallet are you using? If you're using a wallet that generates addresses deterministically, then it could be possible to generate the addresses you don't have in your unencrypted backup.

[x-creature]

It is Bitcoin Core wallet. It does not have HD keys, as they were not implemented back in time when I created my wallet.

One more thing (correct me if I am wrong). By default, Bitcoin Core generates you 100 unencrypted non HD keys (older versions). When you encrypt your wallet Core adds 100 more keys and encrypts the rest. After encryption you have 200 keys. Previous keys, that were initially unencrypted, are not in use anymore, but you can still spend balance from them.
Is my way of thinking right?