VB in Access 2013

[MC42015]

I am trying to use the where condition to assign the caption to the form I am opening through DoCmd.OpenForm triggered by command button OnClick.
This form is a template I assign 4 different record sources (you'll see in part of the code), the caption in property sheet is blank.
I would like it to show me different captions depending on the button I pushed to open
Sample code of two of the buttons I've written so far:

Private Sub cmdCO_Click()
   DoCmd.OpenForm "qdffrmINVMF3713", , , Form.Caption = "Cost Open"
   Forms!qdffrmINVMF3713.RecordSource = "qryISSUE1costopen"
End Sub

Private Sub cmdPP_Click()
    DoCmd.OpenForm "qdffrmINVMF3713", , , Form.Caption = "Partial Payments"
   Forms!qdffrmINVMF3713.RecordSource = "qryISSUE2ppfrm"

End Sub

(I also tried Me.Caption but that didn't work)

Form is opening with proper record source, but I can't get the where to trigger
Imagine I am missing syntax?

Thank you!

[Nauticalgent]

On the form's OnOpen event, try:

Select Case Me.RecordSource
     Case "qryISSUE1costopen"
          Me.Caption = "Cost Open"
     Case "qryISSUE2ppfrm"
          Me.Caption = "Partial Payments"
     Case Else
End Select

[NeoPa]

You seem to imagine that you can simply write an expression after a few commas (,) and the procedure will necessarily process that for you intelligently. It really doesn't work that way at all.

DoCmd.OpenForm( ) has a set of parameters, many of which are optional. The seventh parameter is called OpenArgs and can be used to pass a string across to the Form. Let's forget about positional parameters though (See How to Use Named Arguments). They're just a problem waiting to happen for procedures like this one.
Use something like :

Call DoCmd.OpenForm(FormName:="qdffrmINVMF3713" _
                  , OpenArgs:="qryISSUE1costopen;Cost Open")

That way, in your Form_Open() event procedure you can include :

Private Sub Form_Open(Cancel As Integer)
    Dim astrOA() As String

    With Me
        astrOA = Split(Nz(.OpenArgs, ""), ";")
        If UBound(astrOA) < 1 Then
            Cancel = True
            'Error message if required.
            Exit Sub
        End If
        .RecordSource = astrOA(0)
        .Caption = astrOA(1)
    End With
End Sub