For words that only have three letters, there's no 4th letter. As an example with the word “increase”, there isn't any a lot more letters Later on and thus need to be the word "insert". The word “addict” is in the BIP39 wordlist however you would have used “addi” for https://ilovebookmark.com/story18883461/how-much-you-need-to-expect-you-ll-pay-for-a-good-valid-bip39-seed-phrase