Custom numbered list not continuing in another document

I have approx 30 chapters in separated in individual files with Chatper 1 as a style source.
I have added all the chapters in a book file. Total of approx 30 files in a Book.

Paragraph styles in each chapter
Heading
Body

Each chapter has approx 10-20 headings.

What I want is to give Paragraph number to each of the Heading and I want them to continue accross other chapters. eg. Heading 1 to Heading 10 in Chapter 1. (In one file)
Heading 11 to 25 in Chapter 2 (This is in another file)
Heading 26 to 38 in Chapter 3 (yet another file)

I edited Heading para style and gave a numbered list with custom list named "mylist".

I synchronised the styles in the Book and Applied the heading styles to all the headings in chapters 1, chapter 2 and chapter3 ...

Issue is that all the heading number is getting reset in Chapter 2 and so on. Till chapter 1 its working fine.

Level is 1
Mode in Numbering is "Continue from Previous Number"

I created custom list so that it can be carry forwarded but it is not working for some reason.
Any light on this would be helpful.

If this works, I would like to use the same list "mylist" for subheadings also.

Thanks