If you sync NProd with a refreshed CS, then the changes in NProd OTDS will be applicable. But sywon'tstem won't result in duplicates.
however ACL Permission model will be of PROD data, because OTDS dont control it. So ensure your nprod OTDS users, Groups & Prod ACL has right links.
in OTCS user duplication is not allowed/possible. its a db level unique constraint issue.
in OTDS user duplication is possible(in different paritions ) - but will result in auth failures