Outline Lists
On the Format>Bullets and Numbering>Outline Numbered dialog, the four samples that do not show the word "Heading" in their pictures are not, by default, associated with styles.
These templates produce outline list paragraphs. We used to know such lists as multi-level numbered lists. You use the Promote and Demote buttons to change the levels of the paragraphs. When you do, you change both the numbering level and the indentation.
Unless you create them using styles, and define the styles using VBA, Outline- numbered list paragraphs will break pretty much every time you close the document unless you happen to be a highly-skilled user such as a technical writer who understands all the stuff you read here and bears it all in mind every minute they work! If you do that, the numbering will break only about half the time {grin}.
When you define such a list using Customise, you get the choice of associating a different style with each of the nine levels, or associating just a single style with all levels. If you decide to associate only a single style, ensure that it has its level property set to "1", and that it is associated with the first level.
When a corporate user is creating numbering, they are likely to do it with either AutoFormatting or Format>Bullets and Numbering.
AutoFormat converts the list format the user types into a Word numbered list. Unless the user is sufficiently accurate to type exactly the same format each time, AutoFormat tends to add a new List Template each time the user creates a numbered list.
In a major behind-the-scenes change, in Word 2000, Outline Numbering became the default type of numbering. In earlier versions, clicking the default "Numbering" button on the Formatting Toolbar would produce a Numbered list. It now produces an Outline Numbered List. You would never notice the difference if nothing ever went wrong. Unfortunately, things do go wrong, and when they do, the complexity of the problem is indescribable; made worse by the fact that you have no idea what is going on.
Format>Bullets and Numbering invites you to select a numbered list each time. Most people will select the same list each time, so in a document produced with Format>Bullets and Numbering, the document is likely to contain just a single list. Each time you want a new numbered list, you select the format, then right-click the first item and choose the "Restart Numbering" option. The single list contains multiple restarts.
If multiple users have edited the document, it is likely to contain both multiple lists and multiple restarts. Regardless of which technique each person employs. Each individual user's numbering is different. Word stores its numbering formats in the Registry, so each user has their own. No two are ever the same.
If multiple users use AutoFormat... well, you work it out! The results are pretty close to random.