In many record sets an ancestor’s name should appear only once, but there are exceptions.
People get “double counted” in census records regularly–sometimes because they moved and other times because they had two residences.
In some cases amended birth or death certificates may be filed. This is sometimes done with birth certificates for adoptions and with death certificates if the cause of death needs to be changed.
People can easily be listed on property tax rolls in more than one location if they own property in more than one location.
And individuals (or even couples) can appear as a bride or groom on more than one marriage record.