I would think you would have to know what your downstream style is so you would know what parent to look for upstream. Say the first thing on a page is a Note box and the step after the Note (downstream) is B. (Heading 4). I would need to look upstream for the last Heading 3 (say 6.1.4) and make a cross-reference to it. Another example would be where the first step is 3) (Heading 7) and I would need to cross-reference to the preceding Heading 6 so my continuation header would look something like 6.1.4.B.2.a. If you look at the Headings I listed in the question, you notice the is no period at the end of the Heading 3 numbering. When we manually cross-reference we get 6.1.4B.2.a. with no period added between the 4 and B. I can't find a solution for that either.