Having had 3 rescue cockers, I can assure you that they don't wag ALL the time, only when they are happy.
Violet is my third rescue cocker and the first one I have had with a tail.
When you adopt a rescue cocker, you wait and wait with bated breath for that very first wag. In their previous life, they had very little (if anything) to wag about, so tail wagging is a new experience for them.
It is so wonderful when they wag for the first time
. Then you wait for the next time, sometimes it takes a while because they are so mixed up, they don't know if they might get punished
.
Once they feel secure in their new home, they start to wag most of the time, like most cockers do, but that very first wag remains the most rewarding
Violet still doesn't wag on her first visit to new places, I'm trying to take her out & about a lot and she feels insecure in places she hasn't been before, but she's getting there