Second highest date

You probably get the result your looking for when you use group by and an index column to get an index per group.

In your use case you get an index per serial number. Look at Radacad's explanation on how to do this;

https://radacad.com/create-row-number-for-each-group-in-power-bi-using-power-query

After this step you can use the if function to fill the columns. For example

If index = 1 then initial‐funding date else null

Second funding date column will be

If index = 2 the initialfundingdate else null