The best way I know to "check" radiometric ages is to date a rock using more than one isotopic system (e.g. K-Ar and U-Pb) and compare the ages that you get. If you get the same age from isotope systems with different decay rates and systematics, that is strong evidence that your technique is working.
People have done this many times, and most of the error comes from different levels of uncertainty in the decay constants from one system to another. Many of the decay constants have not been updated for decades (e.g. Steiger and Jager 1977) and are suspected to be a few percent off, but the people who are qualified to make such measurements (physicists + chemists) aren't the people who want to use them in applications (geochronologists and geochemists). So the incentives aren't aligned and I doubt anyone will ever fix them.
Note: Was a geology/geophysics PhD student until recently.
People have done this many times, and most of the error comes from different levels of uncertainty in the decay constants from one system to another. Many of the decay constants have not been updated for decades (e.g. Steiger and Jager 1977) and are suspected to be a few percent off, but the people who are qualified to make such measurements (physicists + chemists) aren't the people who want to use them in applications (geochronologists and geochemists). So the incentives aren't aligned and I doubt anyone will ever fix them.
Note: Was a geology/geophysics PhD student until recently.