Gather list of all IDs ordered by submission date and ID by parsing file path
here is a solution that uses ...    

-Filter instead of -Include
this is usually faster since the filtering is done by the provider [the filesystem in this case] instead of by the cmdlet.    

[PSCustomObject] object construction
faster than Select-Object for building custom objects, since it does not require building/tearing-down a pipeline. plus the Select-Object cmdlet has a great deal of complex logic that is not needed here.    

$AgencyList = foreach ($FL_Item in $FileList) loop assignment
this is VASTLY faster than $AgencyList += for large collections, but only slightly faster for small ones.    

$SourceDir = $env:TEMP
$Filter = '*itunes*'
$TargetYear = 2019
$ExportFile = "$env:TEMP\jasonmadesomething_AgencyList.csv"

$GCI_Params = @{
    LiteralPath = $SourceDir
    Filter = $Filter
    File = $True
    Recurse = $True
    }
$FileList = Get-ChildItem @GCI_Params |
    Where-Object {$_.LastWriteTime.Year -eq $TargetYear}

$AgencyList = foreach ($FL_Item in $FileList)
    {
    [PSCustomObject]@{
        # i don't have any suitable directory info
        #    so i used the BaseName of the file
        Agency = $FL_Item.BaseName.Split('.')[0] -replace '^Itunes_', ''
        LastWriteTime = $FL_Item.LastWriteTime
        }
    }

# this gives a list sorted by ...
#    Agency [alfa sorted 'A' to 'Z' and/or '0' to '9']
#    LastWriteTime [oldest 1st]
$AgencyList = $AgencyList |
    Sort-Object -Property Agency, LastWriteTime

# on screen
$AgencyList

# to CSV
$AgencyList |
    Export-Csv -LiteralPath $ExportFile -NoTypeInformation


truncated on screen output ...   

Agency                  LastWriteTime         
------                  -------------         
AlbumAutoRating_Disable 2019-01-07 12:22:00 PM
AlbumAutoRating_Disable 2019-01-14 12:20:36 PM
AlbumAutoRating_Disable 2019-01-21 12:20:41 PM
AlbumAutoRating_Disable 2019-01-28 12:22:14 PM
AlbumAutoRating_Disable 2019-02-04 12:21:55 PM
[*...snip...*] 
R-PC-SC_Save            2019-01-24 12:38:09 PM
R-PC-SC_Save            2019-02-07 12:37:53 PM


truncated CSV file content ...   

"Agency","LastWriteTime"
"AlbumAutoRating_Disable","2019-01-07 12:22:00 PM"
"AlbumAutoRating_Disable","2019-01-14 12:20:36 PM"
"AlbumAutoRating_Disable","2019-01-21 12:20:41 PM"
"AlbumAutoRating_Disable","2019-01-28 12:22:14 PM"
"AlbumAutoRating_Disable","2019-02-04 12:21:55 PM"
[*...snip...*] 
"R-PC-SC_Save","2019-01-24 12:38:09 PM"
"R-PC-SC_Save","2019-02-07 12:37:53 PM"