Word, insert a multi-level list, but changed it to 1.1, and the 2.1 in Chapter 2 also became 1.1...

The core issue is that Word's multi-level list feature is not a simple sequence of independent lists but a single, field-driven numbering scheme linked to paragraph styles and outline levels. When you manually altered the first instance of "2.1" to "1.1," you effectively reset the sequence for that entire list level, causing all subsequent paragraphs formatted with the same list level (e.g., Level 2) to restart at 1. This occurs because Word interprets your manual override as a command to restart numbering, and its automated field linking propagates that change forward. The software is behaving as designed, albeit in a way that is often counterintuitive to users expecting more manual, discrete control over numbering.

To resolve this, you must avoid direct manual edits to the number itself. Instead, you need to use Word's list formatting controls to redefine the starting point. First, right-click the erroneous "1.1" that should be "2.1" and select "Restart at 1" from the context menu—this may seem contradictory, but it engages the proper control. If that option is not present or does not work, place your cursor in that paragraph, go to the "Home" tab, click the arrow next to the numbering button to open the "Define New Multilevel List" dialog. Here, you can explicitly set the starting number for that level. Crucially, ensure the "Restart list after" option is correctly configured to link Level 2 numbering to the Level 1 heading (e.g., restart after Level 1), which establishes the proper dependency where a new first-level heading (like "Chapter 2") resets the second-level counter.

For a persistent or complex document, the most robust solution is to attach your multilevel list to dedicated paragraph styles (like Heading 1, Heading 2) through the "Define New Multilevel List" dialog, linking each list level to a specific style. This creates a stable, style-based hierarchy rather than relying on direct formatting. Once this linkage is established, you apply the "Heading 1" and "Heading 2" styles to your chapters and subpoints; the numbering will then behave predictably, automatically generating "1.1," "1.2," then "2.1," "2.2," and so on as you apply the styles in sequence. If the document is already corrupted with manual numbering overrides, it may be necessary to clear all numbering (select text and use the "Clear All Formatting" command or remove numbering via the numbering button) and then reapply the properly linked style-based list from scratch to ensure clean field codes.

The broader implication is that Word's list numbering is a field-based system requiring procedural correction through its dedicated interfaces, not manual text edits. Success depends on understanding that the displayed number is a calculated result of underlying settings for list level, restart instructions, and style linkages. Direct typing on the number destroys this link and causes cascading errors. Mastery of the "Define New Multilevel List" dialog and style linkage is therefore essential for any document requiring consistent, automated multilevel numbering, as it moves control from fragile manual intervention to a structured, rule-based format.