I’ve yet to see an official announcement from Sonos in these forums about this. Have you looked on their normal sales oriented web site for the promotion?
To quote directly from that page:
Offer valid on qualifying sonos.com purchases made October 1-31, 2020 for new Disney+ subscribers. Sonos Terms and Conditions apply. Disney+ Subscriber Agreement applies. Credit card required for Disney+ account.
Ya, I see. Just not cool on Sonos’ part to not allow people access to the promotion who have already invested in an ARC, SUB, etc a couple of moths ago.
I’ve never seen a promotion in any company that is retroactive.