I think it would be best if you could choose to have a new subscription start AFTER an existing subscription (on the same device). Recently, I received a free month with purchase, and when I redeemed it, it replaced an existing subscription I already had, and I lost a few weeks of that subscription. Or, when redeeming a subscription code, have it be a subscription “credit” that can be activated later, rather than being activated immediately.
Yep, this is a big issue. You’ve paid for one subscription; the other ought to be added onto the first, not replace it. This type of thing creates bad customer relations.
I just received an emailed offer for a multiple-camera discounted subscription, but I’ve just recently paid for yearly subs for two of my five cameras. The email says NOTHING about how the new subscription will be applied, but by now, I know better.
Related issue: ordering a camera, that comes with a 1-month subscription, but the subscription starts on the day the camera was ordered, not when it was activated.