Given the actual situation you quote no doubt you are right.
Now consider this. There are a group of good players in my area. One of them, Ralph Churney, I cannot ever remember playing with. Since I have known him as a good local player for nearly thirty years I probably have played with him but not in the last eight years or more.
Let's say I play with him next Tuesday - that's not impossible, since I am due to play in a competition, my partner is unavailable, and I am allowed to bring along a substitute. We will have very little time for discussion.
Suppose on the second board the bidding goes 1
dbl redbl - what do I do if the double is penalties?
The answer is that I would alert it, and say "I have no particular agreement with this partner, but it is normal to play this as SOS". Then I will take it out - and I bet you I will be right!.
We have an implicit agreement not from partnership experience nor from discussion but from knowledge of what people play locally.