Many samples reported as "modern" have levels of radioactivity that are indistinguishable from modern standards such as oxalic acid. Due to contamination from bomb testing, some samples are even more radioactive than the modern standards. Other very young samples may be given maximum limits, such as <100 years. Very old samples may be given minimum limits, such as >40,000 years. The very old samples have such low radioactivity that they cannot be distinguished reliably from the background radiation. Very few laboratories are able to measure ages of more than 40,000 years.

Most laboratories use a 2-sigma criterion to establish minimum and maximum ages. In keeping with its practice of quoting 2-sigma errors for so-called finite dates, the Geological Survey of Canada uses a 4-sigma criterion for non-finite dates.