Moving Data Between Subforms & "master Container Form"

Hi there. I need a way to pass data between forms, and subforms. I have "form1" which simply contains a text box requiring the user to input an ID which I will call "PID". it also has a button which has the following code:

Private Sub Command5_Click()
On Error GoTo Err_Command5_Click

Dim stDocName As String
Dim stLinkCriteria As String
stLinkCriteria = "[PID]=" & Me.PID
stDocName = "TestExam"
DoCmd.OpenForm stDocName, , , stLinkCriteria

Exit_Command5_Click:
Exit Sub

Err_Command5_Click:
MsgBox Err.Description
Resume Exit_Command5_Click

End Sub

On the form testExam, I have a page control with 3 separate tabs. For each tab, I've embedded three separate subforms. All forms involved, including the container form (testExam) are bound to separate tables. All tables have one common field - PID
I'd like the user to only have to input the PID on one form, and have it trickle down to all subforms.

In the FOrm_Current sub of the testExam form, I have the following code:

Private Sub Form_Current()
[PID] = Forms!frmForm1.PID
End Sub

Using this code, I am able to pass the data from Form1 to testExam, have the PID on testExam filled in and on tab 2. But tab 1 will not populate automatically. I have no idea why. I don't know where to start troubleshooting this.
Please help.

Is this even a good way to pass data between subforms?