How to return column header based on a value from a table

Hi guys,

I'm looking for a formula which returns the date a precast concrete element has to be placed on the construction site. This way i can check if some elements needs to be produced earlier.
In a previous post, i already found part of the solution. Unfortunately it also returns a date for the elements that are not yet planned or don't have to be planned. For these elements, i would like to return "".

This is the current formula i use:

Formula:

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In the attached file, i reduced both plannings to 10 days instead of 200 . In the tab 'Match' all concrete elements are listed.

Thanks for the help protonLeah. This works great!