Who said it is not a legitimate possibility? That's not how science works. Out of the goodness of my heart, I gave it legitimate possibility. Regardless of the supposed rate of change of the laws of physics, if we measure with same state against changing state we would expect to see an uneven distribution of the data. We don't see that.
This is not an answer. You initially framed the problem by
assuming that those who believed that the laws of physics had changed were arguing for a
sudden change in the laws of physics. That argument seemed plausible even though you did
not really defend it fully. To wit:
This means that psdt should never return a result between T and T + mo, in other words a gap in the age of all items ever tested.
There is no such gap.
Well, how do you know there is no such gap? You talk about "how science works". Need I remind you that science requires evidentiary support for claims like this.
Even so, I suspect you would be right
if, repeat if, your opponents were arguing for a sudden change.
But you have not adequately dealt with the possibility that the change has been
gradual.
The essential issue here is whether the assumption that the laws of nature have changed with time can be
undermined by the evidence. You have given no evidence at all that the available evidence undermines the possibility of a
slow change in the laws of physics.
You are not making your case. I happen to agree with your conclusion, but I don't see how your particular argument makes the case.
Your argument might indeed "generalize" to deal with slow change, but I really don't see how you have made that case.