For words that only have 3 letters, there isn't any 4th letter. For instance with the word “increase”, there won't be any additional letters afterwards and thus should be the word "increase". The word “addict” is inside the BIP39 wordlist however , you might have made use of “addi” for https://bookmarkcolumn.com/story18619592/ledger-seed-phrase-bip39-no-further-a-mystery