I am sorry to hear that. But you are their rescuer too. At least they didn't die not knowing love and affection, didn't die not knowing that most humans are kind and good, and didn't die without dignity or in pain from their advancing illnesses.

You are a good person for doing that so in a sense you have rescued ALL those cats. Just because they went to rainbow bridge doesn't mean you didn't rescue them at all. You should be proud that you took a very hard step.