After you've tried setting up and conducting fuzzing (rather than just reading someone else's success stories) you'll see why we cannot assume they haven't. Fuzzing isn't a binary state, you can spend weeks Fuzzing something, and then someone else with a different methodology can find dozens of new bugs.

Fuzzing scripting languages is particularly complicated because the languages themselves have infinite state. The more complicated the Fuzzer the more coverage it has, but even writing a bespoke language specific Fuzzer is about as complicated as creating the language itself.