The age of dino fossils is at least 1,000 times greater than the effective range of RC testing.
You answered your own question here. Such ages are effectively infinity on an RC scale.
The effective range of RC testing IS known.
I am not certain how it is known, and how well it has been verified. But bones that are effectively infinity years old on the RC scale seem an ideal way to verify the upper limit in real world terms. Theory is a good starting point. Verification is better.
Fossils have been dated with other radiometric methods. Only people ignorant and dismissive of the sciences think that radiocarbon dating is the only radiometric method.
And no, I didn’t answer my own question. There is no “an infinity years old”. It’s a nonsense term.