limit records seached in a DB

[Tailgun]

I have a form that the user creates a new record in the DB
He types a Claimnumber in a box then retypes in a second box and I check that they match so I know he hasn't made a typo. However I also must check that the Claimnumber isn't already in the db. Here is the partial code when he clicks a cmdbutton.

Dim cn As ADODB.Connection
Dim rs As ADODB.Recordset
Set cn = New ADODB.Connection
Set rs = New ADODB.Recordset
cn.ConnectionString = "DSN=eDoan;UID=sa"
cn.Open
 rs.Open "Select ClaimNo from tblClaim Where ClaimNo = '" & txtRetypeClaimNo.Text & "'", cn, adOpenDynamic, adLockPessimistic
   If rs.EOF And rs.BOF And txtFields(1) = txtRetypeClaimNo Then
 
go on with the process
 
Else
 
MsgBox etc

It works just fine with no problems. However as the DB grows it will take longer and longer to check for no duplicate Claimnumber. My question is can I somehow code this to only check the last 4000 records in the DB ?

Thanks for any help