View new records on FamilySearch from Portugal, Brazil, Australia, England, Mexico, S Africa, the USA and more for Find A Grave Index!
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What changed in the 1860 U.S. Census? Corrections?
We are never advised of detail like this, so you won't be able to discover whether these are records that have not been published previously, or as you suggest.
I have wasted many hours looking for the additional records that have been added to an existing collection, as they are usually impossible to identify.