How to disable a ribbon button in Excel if a particular worksheet exists with VBA - vba

Question

I'm building an Excel add-in which allows users to interact with PowerPoint and export data. The users have an option to insert a template into an existing workbook via a button in the ribbon. When they click this, the button becomes disabled as you can't have two templates in one workbook.
The user may then save their workbook and come back to it at a later point. My issue is that I need to detect that they have the template inserted into an existing workbook and I do this by trying to detect if a named range exists (called LoadedToken).
The issue I have is that both the onLoad function of the Ribbon and the VBA class Auto_Open launch before a large workbook is fully loaded. Therefore I'm not actually detecting if the template exists and can't actually disable the button.
Is there such a thing as events in Excel which can be called at a worksheet level (like worksheet_open) but detected in a class?
My code is:
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' When the Ribbon loads
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Private Sub OnRibbonLoad(ribbonUI As IRibbonUI)
Set MyRibbonUI = ribbonUI
Dim Authenticate As New AuthenticationClass
On Error Resume Next
' Enable/Disable buttons based on authentication status
If Authenticate.Authentify = False Then
Authenticated = False
Debug.Print ("Unauthorized!")
Else
Authenticated = True
Debug.Print ("Authorized!")
End If
' If the template doesn't exist then disable a grouping on the ribbon
If TemplateExists = False Then
Call RefreshRibbon(Tag:="Grouping1")
Else
Call RefreshRibbon(Tag:="Grouping2")
End If
End Sub
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' Check if the Template sheet is visible and prevent other buttons from working
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Public Function TemplateExists()
Dim Helpers As New HelpersClass
If Helpers.IsNamedRange("LoadedToken") Then
TemplateExists = True
Else
TemplateExists = False
End If
End Function
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' From the Helpers Class - Check if a named range exists
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Function IsNamedRange(RName As String) As Boolean
Dim N As name
IsNamedRange = False
For Each N In ActiveWorkbook.Names
If N.name = RName Then
IsNamedRange = True
Exit For
End If
Next
End Function
Note: The authentication class is just another class to connect to my API.