I've finally worked out how to do it.
In Seller Central, go to listings, click something other than Active on the left.
e.g. Ended.
Click the All Filters dropdown and pick Sold then See Results.
It works but there's a message "We are considering removing the option to view sold listings on this page. Please use the Orders tab to view sold listings."
The Orders section doesn't show watchers, and isn't customisable to add it.
What is it with eBay constantly making their site less functional?
