I read this sentence in a Youtube video that explains the meaning of even if.
She could have paid more, but she'd got the same service.
with even if:
Even if she had paid more, she'd have got the same service.
It appears from the example that "could have" indicates a real event that actually took place in the past - not merely a possibility. (the woman had actually paid more).
Yet it is very confusing when "could have" indicates a possibility like in
"You could have completed it sooner."
So how could we know the real meaning of "could have" in both cases ? For Example:
Simon could have told her.
Did Simon tell her or not ?
Source: Youtube video Minute 9:50