Adding data in column to a cell

An alterative solution is to build a pivot table in Power Pivot. Create a measure to concatenate the Certs.

Here is your file attached showing same and a tutorial on how to achieve this.

https://www.sfmagazine.com/articles/...ble/?psso=true

this can be very effective if you have a large data set. Very quick and easy. Any updates and Refresh All updates your end result.