An article in the Indy (https://www.independent.co.uk/news/science/archaeology/staffordshire-hoard-most-important-find-anglo-saxon-history-archaeology-book-a9179781.html)suggests that the Staffordshire Hoard (http://soa.org.uk/sm/index.php?topic=3712 and elsewhere) was made up of loot captured by the Mercians - possibly by king Penda - in several battles against other kingdoms.
And there's a new online database (https://archaeologydataservice.ac.uk/archives/view/staffshoard_he_2017/), and an imminent book (https://www.oxbowbooks.com/oxbow/the-staffordshire-hoard-60107.html).
Now also
https://www.theguardian.com/culture/2019/nov/01/staffordshire-hoard-archaeologists-academic-research-gold-ornaments