How do I update a single instance of an inherited form without updating the other open instances?

Question

Edited 3/23 to include suggested changes and new information.

I have a vb.net Windows form, rptBase, with a statusstrip and a ToolStripStatusLabel tssl1. Two forms, rpt1 and rpt2, inherit rptBase.

On frmMain I have ListBox1 with:

Private Sub ListBox1_Click(sender As Object, e As EventArgs) Handles ListBox1.Click
    Dim frmRpt As New frmRptBase

    Select Case ListBox1.SelectedIndex
        Case 1
            frmRpt = New frmRpt1()
            frmRpt.Text = "Report 1"
            frmRpt.Show()
        Case 2
            frmRpt = New frmRpt2()
            frmRpt.Text = "Report 2"
            frmRpt.Show()
    End Select
    AddForm(frmRpt)
End Sub

I would like to report the progress of the reports but when I update tssl1.text on report 1 it also updates report 2 and vice versa. How do I update just one or the other?

I have a dictionary and a method to save a reference to the forms

Public Sub AddForm(frm As Object)
    m_dctFrms.Add(frm, Str(frm.FormID))
End Sub

and a method to update the statusbar

Public Sub UpdateStatus(strMsg As String)
    tssl1.Text = strMsg
End Sub

I run the program, open report 1, then open report 2, then run report1.

New information:

The report runs in a background worker. When I call UpdateStatus from the DoWork sub, it works as expected. When I call UpdateStatus from the ProgressChanged sub, it does not.

Private Sub bw_DoWork(sender As Object, e As DoWorkEventArgs) Handles bw.DoWork

UpdateStatus("This works, only one form updated.")

End Sub

Private Sub bw_ProgressChanged(sender As Object, e As ProgressChangedEventArgs) Handles bw.ProgressChanged

UpdateStstus("This does not work. Both form are updated.")

End Sub

Answer 1

maybe a simple form array (+ simplifie a bit your code) :

 Dim arrForm(5) As Form 'set max forms count
   
    Private Sub ListBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ListBox1.SelectedIndexChanged
        If IsNothing(arrForm(ListBox1.SelectedIndex)) Then
            Dim frmRpt As New frmRptBase
            frmRpt.Text = "Report " & ListBox2.SelectedIndex
            arrForm(ListBox1.SelectedIndex) = frmRpt
            frmRpt.Show()
        End If
    End Sub
 
    Public Sub UpdateStatus(intKey As Integer, strMsg As String)
        Dim frm As frmRptBase = arrForm(intKey)
        frm.tssl1.Text = strMsg
    End Sub