I'm back with a further update!

Flights on two bookings were cancelled by SAS on 19 March and I requested a refund for both the same day. After no progress I made a chargeback on my Amex at the start of June and immediately received a credit.

Today SAS refunded one booking themselves, which now means I have had the refund for that booking twice, once via chargeback and once directly. I expect the chargeback credit will disappear once all systems catch up (don't worry, I don't expect to keep it).

So this means they have reached 19 March in the refund queue.