Arnold, J. R., & Libby, W. F. (1949). Age Determinations by Radiocarbon Content: Checks with Samples of Known Age. Science, 110, 678-680.
but basically they compared their computed results to a “curve of knowns” (historically verified objects). Libby recognized an error and revised the method to arrived at the Cambridge Half-life (5730+/-40).
I don't know about thorium 232, but comparing the ratio of uranium 234 and thorium 230 is used as a dating method (one is soluble, the other is not).
Thank you, I will have to look up the paper.