Import-SPWeb preserves ListItemId?

If you're reading this you have my same problem, you don't have an answers to this question, and maybe you need to move a list across site across site collections/web applications/farms without changing the list item id.
Someone says yes, others say no. The answer is that both answers are true, it depends on the preconditions.

Let's start from this article which explains just a little bit how the ContentDB works.
So, let's create a custom list named "Another custom list" and let's populate it with a bunch of items.

Yeah just 3

So let's look what happens in the ContentDB.
At first let's look at the list id, and we can find it with just a select on the AllLists table querying by title.

Aggiungi didascalia

With the list id in your hands you can find all the entry of the items in AllUserData table, which is the repository of all the ContentDB Items (you can also have a look to the composed primary key of the table from the previous screenshot).

Remember something?

Now, let's delete item 1 and create item 4 and 5 and let's see what happends (Please note that Item1 is still in the content db until i delete it from site collection recycle bin). Moreover in the AllListAux i can now see the counter used to give the list item id to the object.

So this is what happens behind the scenes

Mmm.. Aux table

It's now time to export the list and take a look to what SharePoint made, so unzipping the cmp file, i can read this in the Manifest.xml
You can see that every item is serialized in xml, and surpise surprise there is an attribute called IntId, so let's see what happens importing this cmp file in another site collection:

Import-SPWeb http://sp2013 -Path "C:\TEMP\anothercustomlist.cmp" -IncludeUserSecurity -UpdateVersions Overwrite

and the result is that i've now a new list with a new id, but same informations in the AllListAux and AllUserData.

Only GUIDs changed in the import

and only GUIDs

So, even if i'm not showing you the AllUserData table, also ListItem IDs remains the same, so the answer to our question seems to be yes.
But what if i try to reimport? Well, items are not overwritten and i can see that same object are replicated with different list item id which starts from the value in the aux table.
So the answer is no if you are importing in a preexisting list with other items, because you never know what could be the next item id.

Below you can find some code i used to do a final test in order to get a lot of item from a list with more than 6000 items (which is not the one of this example) from the source list and the destination one, in order to do a final compare which led me to understand that Import-SPWeb is something good :)

string siteUrl = "http://sp2013/sites/test";
string listTitle = "Test";
string user = "Administrator";
string domain = "DEV";
string password = "Password";

using (ClientContext clientContext = new ClientContext(siteUrl))
{
 clientContext.Credentials = new NetworkCredential(user, password, domain);

 List list = clientContext.Web.Lists.GetByTitle(listTitle);
 clientContext.Load(list);
 clientContext.ExecuteQuery();

 ListItemCollectionPosition itemPosition = null;
 while (true)
 {
  CamlQuery camlQuery = new CamlQuery();
  camlQuery.ListItemCollectionPosition = itemPosition;
  camlQuery.ViewXml = @"
  
   
   
  
  1000
   ";

  ListItemCollection listItems = list.GetItems(camlQuery);
  clientContext.Load(listItems);
  clientContext.ExecuteQuery();

  itemPosition = listItems.ListItemCollectionPosition;

  foreach (ListItem listItem in listItems)
  {
   Console.WriteLine("Item Title: {0}", listItem["Title"]);
  }


  if (itemPosition == null)
   break;

  Console.WriteLine(itemPosition.PagingInfo);
  Console.WriteLine();
 }
}