The isochron techniques are partly based on this principle.The use of different dating methods on the same rock is an excellent way to check the accuracy of age results.The latest high-tech equipment permits reliable results to be obtained even with microscopic samples.
A recent survey of the rubidium-strontium method found only about 30 cases, out of tens of thousands of published results, where a date determined using the proper procedures was subsequently found to be in error.
One question that sometimes arises here is how can scientists assume that rates of radioactivity have been constant over the great time spans involved.
The differences actually found in the scientific literature are usually close to the margin of error, usually a few percent, not orders of magnitude!
Vast amounts of data overwhelmingly favor an old Earth.
Whenever possible we design an age study to take advantage of other ways of checking the reliability of the age measurements.