For words that only have three letters, there is absolutely no 4th letter. By way of example with the word “increase”, there won't be any much more letters Later on and therefore should be the word "increase". The word “addict” is while in the BIP39 wordlist but you would have https://socialaffluent.com/story4304333/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-seed-phrase-mnemonics-generator