Kristi, your understanding is correct. I've never tried to save seed from green tomatoes. If you have several green tomatoes, you might go ahead and try saving seed from one (the most mature), if none sink to the bottom you'll know the answer to your question. Kindly post the results here so we'll know too. If you use a clear jar or plastic cup you should know in about 3 days whether there are seeds on the bottom. In the meantime, wrap the other green tomatoes in newspaper and let them ripen. Claud