For words that only have three letters, there isn't any 4th letter. Such as with the word “increase”, there isn't any far more letters afterwards and thus have to be the word "incorporate". The word “addict” is within the BIP39 wordlist however , you would have applied “addi” for “addict”. https://nimmansocial.com/story8574523/ledger-seed-phrase-bip39-no-further-a-mystery