For words that have only 3 letters, there is not any 4th letter. Such as with the word “incorporate”, there aren't any extra letters afterwards and so should be the word "insert". The word “addict” is while in the BIP39 wordlist but you would have applied “addi” for “addict”. Mnemonic https://eternalbookmarks.com/story18661154/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-definition