I have a starting csv with sample data like so:

Underlying AllBlue   AllRed
---------- -------   ------
AUD        1/5/2024                
BRR                        
GBP        3/10/2024       
CAD

Today, 4/29/2024, via another process, a new CSV is produced, like this for example

Underlying AllBlue   AllRed
---------- -------   ------
AUD                       
BRR        4/29/2024               
GBP        4/29/2024       
CAD                  4/29/2024

and I’m looking to append any new data found in columns ‘AllBlue’ and ‘AllRed’ only, to the original csv.
Desired outcome would be

Underlying AllBlue   AllRed
---------- -------   ------
AUD        1/5/2024                
BRR        4/29/2024                 
GBP        4/29/2024        
CAD                 4/29/2024 

Notice how the new data from 4/29/2024 csv is overwriting to original. Also, how the GBP/AllBlue cell is updated with the new date.

#sandbox testing
$CSVFiles = Get-ChildItem -Path "C:Sandboxtest" -Filter "*.csv"
 
#put into array
$CSVData = @()

ForEach ($CSVFile in $CSVFiles) {
    $CSVContent = Import-Csv -Path $CSVFile.FullName 
    $CSVData += $CSVContent 
}
 
#output
$CSVData | Export-Csv -Path "C:Sandboxtestoutputcolors.csv" -NoTypeInformation -Append

This appends the data, but doesn’t overwrite the columns?. Ive tried multiple parameters clobber, append.

Thank you for your time.