For words that only have 3 letters, there isn't a 4th letter. For example with the word “insert”, there won't be any a lot more letters afterwards and so must be the word "insert". The word “addict” is during the BIP39 wordlist but you might have utilized “addi” for “addict”. https://bookmarkfriend.com/story19165278/ledger-seed-phrase-bip39-no-further-a-mystery