Doc: IndexOf or IndexOfAsync; How to select an item

[Marco-CH]

.NET Framework 4.6.1
Used with WPF DataGrid

In the source code and at Virtualizing Data with XAML I found following description of the methods IndexOf and IndexOfAsync:
"This returns the index of a specific item. This method is optional – you can just return -1 if you don’t need to use IndexOf. It’s not strictly required if don’t need to be able to seeking to a specific item, but if you are selecting items implementing this method is recommended."

And an example at Virtualizing Data with XAML

public int IndexOf(Author item)
{
    return (from a in _ctx.Authors orderby a.AuthorName where a.AuthorName.CompareTo(item.AuthorName <0 select a).Count();
}

The first problem is that if the AuthorName is not unique in your example, a wrong index is returned. Unless the correct index is returned, the VirtualizingObservableCollection has a problem. Correct?

At Virtualizing Data with XAML you write:
Supports true multi-user read/write without resets (maximizing performance for large-scale concurrency scenarios).
Your example on GitHub is unfortunately read-only. Can you explain how a new element to the collection added and selected? Add to database and call this.VOC.ResetAsync()/this.VOC.Clear() or call this.VOC.Insert(index + 1, newItem, DateTime.Now)? As can be avoided that this element is not double in the list after scrolling?

When I bind the SelectedItem of the DataGrid and reorder the list with a selected item, unfortunately all elements are loaded:
GetItemsAtAsync: 0, 100
GetItemsAtAsync: 100, 100
GetItemsAtAsync: 200, 100
GetItemsAtAsync: 300, 100
GetItemsAtAsync: 400, 100
GetItemsAtAsync: 500, 100
...

Can you please publish an example containing CRUD (Create, Read, Update and Delete) operations? It would be nice if we could see the following operations:

this.SelectedItem = newOrChangedItem; //with implemented -> dataGridOrListBox.ScrollIntoView(dataGridOrListBox.SelectedItem);
this.VOC.Add(newItem);
this.VOC.Insert(index, newItem);
this.VOC.Remove(oldItem);
var item = this.VOC.SingleOrDefault(i => i.ItemID == 120);

If you want you can use my example on OneDrive (VS 2015, .NET Framework 4.6.1, EF 6.1.3).
Thank you very much.