Not sure I understand what you are asking. I understand you own a legacy device that is eligible for a discount. And you bought a new speaker from Curry’s. What happened after this? What do you think will happen to you legacy device?

Not that easy to explain but I will try.  So as I said, I purchased new Sonos Arc yesterday from Currys - awaiting delivery on or about 19 Nov 2020.  I logged into my Sonos account today and even although I did not purchase the Arc through the Sonos website they know I have bought it.

My question/worry is this - are Sonos going to apply the upgrade discount and automatically disable my legacy Play 5?

Thanks, Paul

I would say no. As far as I am aware to benefit from the upgrade program you need to order through the Sonos website. Perhaps you would be better cancelling or returning the Curry’s order and placing a new order with Sonos directly if you want to take advantage of the discount. 

I don't see how Sonos could know about your Arc purchase - but it doesn't matter anyway as even with a discount, devices are no longer disabled and you are free to continue using them.