Understanding word numbering manipulation

I've created a document with two types of numbering references. The first references a style which is linked to a number and the second is linked a style but has manual numbering assigned. I've added an image so you can see what this looks like in word. Note that to the front end user it looks like the only difference is the style.

However in the xml there is a slight difference. Here is an section of document.xml showing the xml for the first set of numbering. Note that the first two lines do not have any reference to a w:numId but the second two lines do. This is because the style "DemoStyle" has a reference to w:numId but only the first level. When I indented lines 3 & 4 they needed to be assigned a new numbering level/w:ilvl. Note that these paragraphs are linked to numId "1"

If you take a look at the styles.xml you will see that DemoStyle is also linked to numId "1"

Going onto the manually applied numbering see the xml below. You can see that the numbering has been assigned to all four paragraphs, not just the indented lines.

In the numbering.xml document you will find these numbering items as w:num nodes. These nodes allow multiple items to reference the same abstract number (not shown in this case but is possible).

The w:abstractNumId then references the w:abstractNum. This contains all the numbering information.

To access the numbering part in a document via OpenXml you can use the following code:

byte[] document = File.ReadAllBytes("C:\Demo Doc.docx");
using (MemoryStream memoryStream = new MemoryStream())
{
  memoryStream.Write(document, 0, document.Length);
  using (WordprocessingDocument wordprocessingDocument =     WordprocessingDocument.Open(memoryStream, true))
  {
     NumberingPart numberingPart  = wordprocessingDocument.MainDocumentPart.NumberingPart;
  }
}