For words that have only 3 letters, there isn't a 4th letter. For example with the word “incorporate”, there are no more letters Later on and thus have to be the word "include". The word “addict” is in the BIP39 wordlist but you might have employed “addi” for “addict”. Mnemonic https://isocialfans.com/story4380733/ledger-seed-phrase-bip39-no-further-a-mystery