..... Not knowing about something isn't a defence!
It is. If the council can prove in court that they have taken reasonable means to maintain the road such as periodic inspection as deemed appropriate for the type of road / traffic etc and no one has reported the pothole then what can you realistically expect them to do about it? Is it reasonable that they should have a crystal ball?
With the scheme I wouldn't advocate there is the danger that the council is efficient and fill it in quickly thereby denying you the ability to claim. Round these parts they seem to take ages to sort them out, and I know they have been reported, but I guess its down to how busy the road is / individual councils etc.
Its unfair because if the road fell apart that quickly then the chances are it in a pretty bad state to begin with, but that doesn't really help the claim unless it was extreme.