Surely you have a business rule for this? Is data with duplicate keys allowed or not allowed (the answer might be different depending on the table)? If it is allowed then your DB2 table definition is incorrect and needs to be corrected. If it is not allowed, then your current Production data is incorrect and your new DB2 data is correct.
"Data architect designed that so keys allowed to minimize data" - this isn't a business rule, it's an architectural decsion. I suggest you raise the issue of a lack of a business rule with your project team. Until you decide what this rule is you don't know if your migrated data is correct or not.
If only observations (records) were removed where all values (variables,columns) were identical, then no information was lost, and you should ask yourself where the duplicates came from.
If this is not the case, then information WAS lost, and you have to determine if this information is crucial, and how to make sure the correct "duplicate" is kept if information can be discarded. If information is crucial, the key architecture needs to be reviewed.
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