For words that only have three letters, there is not any 4th letter. One example is with the word “increase”, there aren't any far more letters Later on and so needs to be the word "incorporate". The word “addict” is in the BIP39 wordlist but you would have applied “addi” https://captainbookmark.com/story18941798/new-step-by-step-map-for-ledger-seed-phrase-bip39