For words that only have three letters, there isn't any 4th letter. For example with the word “increase”, there won't be any more letters Later on and thus must be the word "include". The word “addict” is while in the BIP39 wordlist but you would've applied “addi” for “addict”. In https://bookmarkpagerank.com/story18813339/the-5-second-trick-for-ledger-seed-phrase-bip39