Dear Tech Team, is there any way of retrieving an old license with just the hardware serial number of the CF card?

Thank you 

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Split from Upgrade from Simotion D435 to D435-2 .

Yes of course. 

Just go there 

http://www.siemens.com/automation/license

click on "Display License key" in the left bar menu.
Insert just the HW Serial number of the CF and click "Show License key".
If there's some license "connected" to that CF card you can download them as keys.txt.

Then you can put them in the KEYS folder of the CF card (with a CF card reader of course).

EDIT: you should set english language from the top right of the page