AD8602ARZ-REEL7 lead frame issue

We have a question about that our company have purchased the product P/N: AD8602ARZ-REEL7 with different date code ( DC: 1803 and 1909) such as the above X-ray picture. 
We found that they were different lead frame of this parts with different date code, but We could not find related product change notice from your website. 
Our company would like to know more detail from your as OCM to avoid any counterfeited parts issue. 

Could someone please comment and let us know more about why the lead frames with this 2 date code are different?

Thank you

Revised for the question
[edited by: Smith-HK-ACHO at 9:27 AM (GMT 0) on 16 Jul 2019]