C. nankingense looks like the best match. C. nankingense is a synonym for C. indicum. There are 5 different varieties of C. indicum, and I suspect they differ in leaf shape and petal count. There aren't any online photos or illustrations of the varieties to compare with your plant. Coincidentally, some internet photos that have it labeled C. nankingense have matching leaves to your plant, but I don't know which variety those photos are of. It's had several different names in the past. It's edible too. The globe shape and late blooming cold hardiness matches C. indicum also.

http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=220002857

The Kew / Plants of the World Online page on this plant accepts only 2 varieties. One of which is var. indicum. In other words the typical species, with its 34 synonyms.

Chrysanthemum indicum L. | Plants of the World Online | Kew Science

Note to self, always check the Kew website. 😁

I assume Kew reflects the most current scientific thinking, but I came across this fairly recent research article that refers to C. nankingense and C indicum as separate species - Origins of Cultivars of Chrysanthemum - where it says, " The wild species C. indicum, C. zawadskii, C. dichrum, C. nankingense, C. argyrophyllum, and C. vestitum were likely directly or indirectly involved as paternal species of most of the chrysanthemum cultivars examined in this study." Figure 1 in the article includes leaf photos of a number of species and cultivars, and the leaf of C. indicum is much more deeply lobed than the leaf of C. nankingense. The article also seems to indicate that C. nankingense is diploid, while C. indicum is tetraploid (?)

Whatever its taxonomic status, it would probably have marketable value as a very late season hardy perennial that is highly attractive to pollinators (and apparently edible as well), but I don't think I've ever seen it for sale anywhere. I'll have to ask the property owner where they obtained it.

It makes sense that nankingense should be at species rank. The leaves in your link match your plant perfectly. I don't understand why there are 2 completely different taxonomic treatments floating around the internet. What is labeled as nankingense looks distinct enough to have species rank. I don't understand why it now seems to be lumped into Chrysanthemum indicum? World Flora online doesn't recognize nankingense either. I'm going to search for more answers. It comes from China, which makes it more difficult.

http://www.amwayabrc.com/about.htm