Bip39 possible combinations https://edgargvkh682.theburnward.com/a-novice-s-overview-to-getting-a-bip39-mnemonic-expression Though it utilizes BIP32 approach you are able to even now import BIP39 seeds into Electrum wallet. Also other than BIp32 There exists BIP44 version which some wallet use for your technology of seeds. For words that only have 3 letters, there is no 4th letter. https://210list.com/story21197892/bip39-mnemonic-online-5-essential-elements-for-bip39-word-list-pdf-https-www-youtube-com-channel-ucupxfytj0fb78sq55hu6ocw