Thank you Hans!
One of these days I need to properly learn CSS... ;-)
I have edited Exported CSS files before, but my sophistication in this is just as a blind hacker.
So, this suggests that the support for the generation of the CSS code for cell styles with automatic numbering objects (and it seems for embedded counter objects in cells--I tried a simple example of this and it didn't work, though I need to do more testing) is lacking.
I will file a bug report on this...