That's circular reasoning if I've ever seen it. Note that I myself don't think that half-life rates change, but your notion of proof just isn't.
"Those observations show that the physical constants of the universe are not more that a few percent different than they are today."
No, those observations ASSUME that the physical constants of the universe are not more than a few percent different than they are today. Many scientists have said quite bluntly that gradualism and uniformitarianism are required ASSUMPTIONS in order to reasonably to historical scientific research. They are ASSUMPTIONS not conclusions.
"Again, realize that all of the dating mechanisms overlap and correlate."
Incorrect. They often differ by as much as tens or hundreds of millions of years. In those cases, the date which matches the scientists expectations (i.e. evolutionary theory) is chosen.
"Probability has no dog in this hunt, as it has all been removed by the correlative date samples."
Correlative date samples IMPOSE bias, they don't remove it.
Cite a specific example, please.
No, the observations that I allude to make NO assumptions. For example, if the fine structure constant changes by more than 1% or so, then fusion reactions begin having problems and certain types of stars have problems burning, reactions that we can see occurring through spectral analysis of early-universe galaxies. Instrumentation is getting refined enough to handle observations of See this for example, or this.
Do you think scientists are just kidding when they say "Question everything"? In some cases, assumptions are made because no one has yet come up with a way to accurately test it. Until recently, we didn't have ways to test some of this stuff.