One obvious example is that you can continue monitoring for evidence of attempts to use the vulnerability. A delayed honeypot, so to speak.
In other words, you don't have evidence that this vulnerability wasn't abused in 2 weeks, you have evidence that no one abused it in ~6 months. Still not perfect, but a more compelling argument that it wasn't abused.
In other words, you don't have evidence that this vulnerability wasn't abused in 2 weeks, you have evidence that no one abused it in ~6 months. Still not perfect, but a more compelling argument that it wasn't abused.