For words that only have 3 letters, there is no 4th letter. For example with the word “insert”, there are no a lot more letters afterwards and thus should be the word "include". The word “addict” is while in the BIP39 wordlist however , you would have applied “addi” for https://bookmarkangaroo.com/story18916384/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-definition