I am writing a non-fiction book. I am not writing the chapters sequentially e.g. the first chapter first and then second etc. I have started with the sixth chapter and now writing the second chapter. As a result, the references in the sixth chapter start from 1 to 13 and now the references in the second chapter start from 14. Is this allowed? Do the references need to be in the order of chapters? If no then how do I arrange my references in an MS Word (.docx) document as I am writing?
There are a number of different ways this issue is handled in practice. The most common is for each chapter's references to be placed at the end of the chapter and to start from 1 again for each chapter. I have also seen works that have all references throughout the book included in a single, continuous numbering system, but this is far less common.
The easiest way to handle a non-fiction work that is reference heavy in MS Word would be to create each chapter as a separate document, then create your main document as a merge template. If you do it correctly, swapping chapters/paragraphs etc. around will see your numbering systems updated automatically.