CTD,
what Nr do you allow during OEI training then? In the real case of an engine failure you can droop to 91% Nr, surely the 97% is a 'normal' limitation? A topping check is not a 'normal' operation and consequently I would have thought it was acceptable to droop below 97%. The reason being that if, for some reason, you have slightly wrongly adjusted beep ranges, lazy N2 governors or a misadjusted droop compensation cam (or all 3) it is easily possible to reach 97% Nr on one engine without achieving topping. Pulling to, say, 94% will confirm without doubt whether the engine is indeed topping at the correct figure or less. It is also possible to achieve the correct N1 at 97% Nr, but not be sure whether in fact further application of collective will increase the N1 further ie it is not topping.
I stand back awaiting correction.