For words that have only 3 letters, there's no 4th letter. For instance with the word “increase”, there won't be any far more letters Later on and therefore must be the word "insert". The word “addict” is inside the BIP39 wordlist however , you would have applied “addi” for “addict”. https://health-lists.com/story19417883/the-greatest-guide-to-seed-phrase-bip39