Skipping Macro's

I have a masterlist in Excel with macro's to pull information from 20 other lists which are identical in format to the master but will contain different information on each (20 different users inputting on diff lines). The lists will have unique names such as P1, P2, etc.

It is working great. However the only issue I have is that sometimes a user may not have anything to enter so I might be missing a sheet. Is there a way to adjust the macros so that it can skip over a record if it's not present or must I have a "dummy list" opened for any which are missing? Below is a copy of the macro that I'm using if that helps. This is repeated for P1 up through P20.

Thanks for advance to any help you can give this brain-weary woman!
Terry

[vba] 'Sheets("Instructions").Select
'Range("C9").Select

'TotRows = ActiveCell.Value
'TotRows = TotRows + 1
Sheets("Prop Base").Select
Range("Q2").Select

Windows("P1.xls").Activate
Range("Q2").Select
'Rows = 2
Do Until ActiveCell.Value = ""
If ActiveCell.Value = "y" Then
Selection.Copy
Windows("MasterList.xls").Activate
ActiveCell.Select
Selection.Paste
End If
Windows("MasterList.xls").Activate
ActiveCell.Offset(1, 0).Range("A1").Select
Windows("P1.xls").Activate
ActiveCell.Offset(1, 0).Range("A1").Select
Loop

'Windows("P1.xls").Activate
'Range("Q2").Select
'Selection.Copy
'Windows("MasterList.xls").Activate
'Range("Q2").Select
'Windows("MasterList.xls").Activate
End Sub[/vba]