For words that have only three letters, there is no 4th letter. Such as with the word “insert”, there aren't any more letters afterwards and therefore need to be the word "increase". The word “addict” is during the BIP39 wordlist but you would have employed “addi” for “addict”. If you're https://guidemysocial.com/story4554951/an-unbiased-view-of-bip39-seed-phrase-github