ModID is meaningless with the ValueList structure. It is just another item in the row list, it is not a hidden column.
Fix the Lookup in table field and also in the listbox. This means remove the ModID item and the empty rows or use a table as RowSource.
Then should not need the -1 calc. However, even before my edits the correct page is not opening. I don't know how this can be working properly for you, the file I downloaded is not.
Set the Multi-Value property of listbox.
Include code: Me.TabCtl1.Visible = True
Consider this version of code that will turn pages on and off.
For i = 0 To Me.Modifications_3.ListCount - 1
Me.TabCtl1.Pages(i).Visible = Me.Modifications_3.Selected(i)
Next
Me.TabCtl1.Visible = True