For words that have only three letters, there is not any 4th letter. Such as with the word “insert”, there won't be any a lot more letters afterwards and thus should be the word "add". The word “addict” is during the BIP39 wordlist but you would've applied “addi” for “addict”. https://socialicus.com/story4257782/helping-the-others-realize-the-advantages-of-bip39-seed-phrase-mnemonics-generator