The obvious hope would be that referring placeholders for numbering streams would be made to work in headers and footers. But I suspect that the system of processing that compile employs precludes this – or is very far from it. So, not a minor tweak!
In inDesign, this sort of thing is handled by a combination of special placeholder variables and defined character/paragraph styles. You can put into the header or footer layout a defined variable which is set to be replaced by the contents of the first/last occurrence of a text span of a certain defined style on any given page.
Making this sort of thing work is obviously a sophisticated business. And that is before we even think about what would be required to effectively pass the results into various file formats (e.g. Word)!
But I certainly agree this would be cool to be able to do.
It’s probably also very likely that a more dedicated scriptwriting program will be able to do this even more easily, such as Final Draft, as a function of a template without having to set anything up. Scrivener is aimed more at the early writing phase, rather than once you start needing to print to some specification. It has some tools for that (mainly aimed at proofing quality output), but it’s not our focus.
For this specifically, the main issue for Scrivener is that it doesn’t really do page layout. It has a little awareness of pagination, but not enough to be adjusting the headers based on the content on the page, from one page to the next (page breaks are an exception and that is why the available placeholders centre around page break based header/footer changes).
I currently have this in header text: <$k> - <$t> - <$p>. But that’s not working.
Well the latter one definitely should be, but the middle one is an auto-numbering placeholder (for “one”, “two”) that would increment every time you used one—or in this case on every single page—definitely not what you want. I don’t know what <$k> is, but all of the placeholders that work in the header and footer fields are documented in Table 24.2, in the user manual PDF.