For words that only have three letters, there isn't any 4th letter. For instance with the word “increase”, there won't be any a lot more letters Later on and so need to be the word "incorporate". The word “addict” is within the BIP39 wordlist however you would have applied “addi” https://worldlistpro.com/story20570134/the-5-second-trick-for-ledger-seed-phrase-bip39