The way we work it at our club is as follows: before you put a comp card up, you can put a practice card up, to make sure your zero is spot on etc. Now, many of us who are what you might call mean, wince at using an expensive BR target card for zeroing, so we put up a plain 17cm square target and zero with that.
Zeroing is done as part of a separate and prior detail; when you take your position in the detail to shoot your ten shots in the card, that's all you do. And no sighters at that time.
Yes the cards are signed by the shooter and witnessed and dated by an approved witness. Neil, you clearly have the same need for diazepam as many of us experience.