Combining in
quadrature suggests a 2 - sigma uncertainty of + -4.4 C for the LGM uncertainty, which doesn't seem ridiculous for a reconstruction based only on SST proxies — bigger than the AR5 estimate of + -2.5 C, but that estimate is based on much more data.
However, the matching of their characteristics as set out in the main text, points a) to c), and the fact that some fluctuations will be reflected in OHU,
suggests a reduction from the 0.11 °C error standard deviation implied by adding two 0.08 °C standard deviations in
quadrature, say increasing halfway, to 0.095 °C.