For words that have only 3 letters, there's no 4th letter. For example with the word “incorporate”, there aren't any much more letters Later on and thus need to be the word "increase". The word “addict” is while in the BIP39 wordlist but you might have made use of “addi” https://mirrorbookmarks.com/story18803393/ledger-seed-phrase-bip39-no-further-a-mystery