Hi there
When I sent my log book off to unfreeze my ATPL (back in 2002) I had the chief pilot sign off as a single instance that all my entries were correct and truthful etc. There was no comeback from the CAA, so I can say
AFAIK that you would not need every P1/S entry countersigned.
I think the old system (before my time) was to count P2 time as half P1/S time, so therefore you would be claiming more "hours" under that system if you were cheating....and therefore the countersignatory was more necessary then.
No doubt someone will correct me if I'm wrong about that
Cheers
WM