You'll notice that both of these links are about identifying decay rates with more precision. In 1907, Professor B. B. Boltwood, radiochemist of Yale University, published a list of geologic ages based on radioactivity. Although Boltwood's ages have since been revised, they did show correctly that the duration of geologic time would be measured in terms of hundreds-to-thousands of millions of years. This continues to be the case. In order for the YEC scenario to be true, scientists must be mistaken about decay rates by factors of 100 or more. That's substantially more error than you seem to have been hoping to identify from your links. What's more, those two strontium isotopes are not used in radiometric dating of rocks because their half-lives are very short; these are toxic products of nuclear reactors (SR90 was a product of the Chernobyl disaster).
According to that first study on SR92, it has a spread of 5% between values, and with a half-life of under three hours. That isotope is 1) rare and 2) REALLY HOT to handle. Errors in decay rate measurement for things like carbon-14 will be smaller. Decay rates for isotopes with longer half lives, i.e. those used to date rocks, are known to within a few percent or better. One of the several reasons that U-Pb concordia-discordia dating is so often used is that the decay rate of uranium is known to much better than a percent. Bombs and reactors tend to attract lots of research money.
Some further info courtesy of "JonF", a scientist who talks at EvC:
from Begemann, F., Ludwig, K. R., Lugmair, G. W., Min, K., Nyquist, L. E., Patchett, P. J., Renne, P. R. Shih, C.- Y., Villa, I. M. and Walker, R. J. (2001). Call for an improved set of decay constants for geochronological use. Geochim. Cosmochim. Acta 65, 111--21:
The decay of 238U and 235U to 206Pb and 207Pb, respectively, forms the basis for one of the oldest methods of geochronology. While the earliest studies focused on uraninite (an uncommon mineral in igneous rocks), there has been intensive and continuous effort over the past three decades in U-Pb dating of more-commonly occurring trace minerals. Zircon in particular has been the focus of thousands of geochronological studies, because of its ubiquity in felsic igneous rocks and its extreme resistance to isotopic resetting.
No decay constant of any radionuclide used for geochronology has been (or, arguably, can be) more-precisely measured than those of 238U and 235U, a consequence of the mode of decay (alpha), favorably short half-lives, and the availability of large quantities of isotopically pure parent nuclides.
Now adding to this, as has been shown in the Geologic Column thread, scientists regularly use more than one dating method in order to verify the accuracy of the dates for the rock samples. The consilience of dates obtained with multiple methods (including U-Pb) using different isotopes with different decay modes is powerful evidence that scientists' dates are correct within a small margin of error.
Some links that demonstrate this:
Radiometric Dating Does Work!Consistent Radiometric DatesAre Radiometric Dating Methods Consistent With Each Other?Are Radiometric Dates Consistent With the Deeper-is-Older Rule?Radiometric DatingRadiometric Ages of Some Early Archean and Related Rocks of the North Atlantic CratonRadiometric Ages of Some Mare Basalts Dated by Two or More Methods
