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In an earlier paper (2007), we used follow-up observations of a sample ofsources from the 9C survey at 15.2 GHz to derive a set of spectral-indexdistributions up to a frequency of 90 GHz. These were based on simultaneousmeasurements made at 15.2 GHz with the Ryle telescope and at 22 and 43 GHz withthe Karl G. Jansky Very Large Array (VLA). We used these distributions to makeempirical estimates of source counts at 22, 30, 43, 70 and 90 GHz. In a laterpaper (2013), we took data at 15.7 GHz from the Arcminute Microkelvin Imager(AMI) and data at 93.2 GHz from the Combined Array for Research inMillimetre-wave Astronomy (CARMA) and estimated the source count at 93.2 GHz.In this paper, we re-examine the data used in both papers and now believe thatthe VLA flux densities we measured at 43 GHz were significantly in error, beingon average only about 70 per cent of their correct values. Here, we presentstrong evidence for this conclusion and discuss the effect on the source-countestimates made in the 2007 paper. The source-count prediction in the 2013 paperis also revised. We make comparisons with spectral-index distributions andsource counts from other telescopes, in particular with a recent deep 95 GHzsource count measured by the South Pole Telescope. We investigate reasons forthe problem of the low VLA 43-GHz values and find a number of possiblecontributory factors, but none is sufficient on its own to account for such alarge deficit.

9C spectral-index distributions and source-count estimates from 15 to 93 GHz - a re-assessment