Perform Operation on AD User Without DN

Question

The unique identifier we use throughout our organisation is the users employee ID which has traditionally been put in to the Initials field on the General tab.
When HR are processing employees that exit the company, they have easy access to the users name and ID but not to their username which unfortunately is not at all what you would call a a consistent format.
I have plenty of scripts that will perform AD operations using the DN, but in this case I need it to look up a user based on their "initials" listed in a CSV and move those users to a different OU.
This is the script I have for doing it with their username but I have no idea if I can just look up the initials field and perform operations based on that instead or if it needs to be a two step process that finds the user, retrieves their DN and performs
the operation on that.
# Specify target OU.
$TargetOU = "ou=NewUsers,ou=West,dc=MyDomain,dc=com"
# Read user sAMAccountNames from csv file (field labeled "Name").
Import-Csv -Path Users.csv | ForEach-Object {
    # Retrieve DN of User.
    $UserDN = (Get-ADUser -Identity $_.Name).distinguishedName
    # Move user to target OU.
    Move-ADObject -Identity $UserDN -TargetPath $TargetOU
}

Answer 1

It's going to be horribly slow if you have to search for each user by initials.  
I'd build a lookup table first, and then work out of that:
$EmpID = @{}
Get-ADUser -Filter * -Properties Initials |
foreach { $EmpID[$_.Initials] = $_.distinguishedname }
# Specify target OU.
$TargetOU = "ou=NewUsers,ou=West,dc=MyDomain,dc=com"
# Read user EmployeeID from csv file ("Initials" in csv)
Import-Csv -Path Users.csv | ForEach-Object {
# Retrieve DN of User.
$UserDN = $EmpID[$_.Initials]
# Move user to target OU.
Move-ADObject -Identity $UserDN -TargetPath $TargetOU
You might want to add a -SearchBase to limit the Get-ADUser if you can.
[string](0..33|%{[char][int](46+("686552495351636652556262185355647068516270555358646562655775 0645570").substring(($_*2),2))})-replace " "