How can I subtract from Duplicate Records?

I need a suggestion on how to execute the appropriate function to get correct the Keep Qty in column D. Any help or suggestions appreciated.

Here is my issue:

I have multiple parts in column A, and there can be duplicates. Qty Return in column B may be a different quantity for each part. Regional Buy in column C will be the same quantity for each Part. See the attachment.

I need to determine the possible amount I can keep from Qty Return based on the Regional Buy Qty and the result will be listed in Column D.

The challenge is that there are duplicate part numbers, which is making it difficult for me to determine the correct formula to use.

I am using the current formula in Column D, and it seems to work until I come across more than 2 occurrences such as in Row 8:

=IF(OR(A2=A1,A2=A3),IF(A2=A1,MIN(C2-D1,B2),IF(C2>=B2,B2,C2)))

Thanks for all of your help.

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