It wasn't a typo and I had just forgotten to use molar fractions.
Here is a reference with values and other references used to calculate the 238U/206Pb.
Miyajima, Y., Saito, A., Kagi, H., Yokoyama, T., Takahashi, Y. and Hirata, T., 2021. Incorporation of U, Pb and rare earth elements in calcite through crystallisation from amorphous calcium carbonate: simple preparation of reference materials for microanalysis. Geostandards and Geoanalytical Research, 45(1), pp.189-205.
The measured 238U/206Pb and 207Pb/206Pb ratios of the samples were corrected using the measured/expected ratios of the glass RMs NIST SRM 612 (for Higher calcite) and 614 (for Lower calcite) analysed in the same sessions. The expected 207Pb/206Pb ratio of NIST SRM 612 and 614 were 0.90726 from Jochum et al. (2005) and 0.87101 from Baker et al. (2004), respectively. The expected 206Pb/238U ratios of the NIST glasses were calculated to be 0.29241 (NIST SRM 612) and 0.80603 (NIST SRM 614) from the mass fractions, isotopic abundances (molar fractions) and atomic weights of U and Pb (Pearce et al. 1997, Baker et al. 2004, Jochum et al. 2005, 2011, Duffin et al. 2013).