Duplicate Customer Numbering

I know this link shows the profiles for numbering

https://support.oracle.com/cloud/faces/DocumentDisplay?_afrLoop=370589017367025&_afrWindowMode=0&id=1992007.1&_adf.ctrl-state=n2fqoqhth_132

But the question is how can we avoid duplicate numbering ? Is there a configuration available for that ?

Is alphanumeric numbering acceptable ?

And as a process ,when we do data migration what should be setup ?