Ah, I misunderstood your statement, I thought you were saying that only 3MF files counted.
Evidently, only 3MF files can count as printed since they store the designer’s user ID in an XML file, which I assume is how the prints are tracked.
Maybe there’s a way to store something similar in the STL’s extra data, like a special image, but that’s just speculation.
Thanks for the clarification!