For words that only have 3 letters, there is no 4th letter. Such as with the word “incorporate”, there isn't any much more letters afterwards and therefore need to be the word "insert". The word “addict” is from the BIP39 wordlist however you would've employed “addi” for “addict”. bip39-phrase.com is https://mirrorbookmarks.com/story18886762/invalid-bip39-phrase-things-to-know-before-you-buy