Connecting calendar ages to radiocarbon (C-14) ages, i.e. constructing a calibration curve, requires C-14 samples that represent, or are closely connected to, atmospheric C-14 values and that can also be independently dated. In addition to these data, there is information that can serve as independent tests of the calibration curve. For example, information from ice core radionuclide data cannot be directly incorporated into the calibration curve construction as it delivers less direct information on the C-14 age-calendar age relationship but it can provide tests of the quality of the calibration curve. Furthermore, ice core ages on C-14-dated volcanic eruptions provide key information on the agreement of ice core and radiocarbon time scales. Due to their scarcity such data would have little impact if directly incorporated into the calibration curve. However, these serve as important "anchor points" in time for independently testing the calibration curve and/or ice-core time scales. Here we will show that such information largely supports the new IntCal20 calibration record. Furthermore, we discuss how floating tree-ring sequences on ice-core time scales agree with the new calibration curve. For the period around 40,000 years ago we discuss unresolved differences between ice core Be-10 and C-14 records that are possibly related to our limited understanding of carbon cycle influences on the atmospheric C-14 concentration during the last glacial period. Finally, we review the results on the time scale comparison between the Greenland ice-core time scale (GICC05) and IntCal20 that effectively allow a direct comparison of C-14-dated records with the Greenland ice core data.