I never found any uncharted reefs
in the pacific, and I know that the french particularly have done an amazing job re-charting their parts
to a very high accuracy level.
But I also know that the Bohemia river in the ches bay has a note on the chart "shoaling reported 1981", and it is in fact significantly shallower than shown, and they have still not changed the depths on the chart. I asked one of the USCG folks responsible for charting the bay about it and she said they only care about/update/have budget
for the areas with commercial/shipping traffic.
So, I would not be surprised if outside the french areas, and the US military use areas, there were still some charting errors/omissions.