On my Classic policy, you do not use any no-claims bonus, nor do you accrue any. They work a price out, check your history (just asked to see it to prove I hadn't had loads of "fault" claims then sent it straight back) and away you go.

I then used the vacant NCB on another car instead. Confirmed with the Classic policy people that it was okay to use that NCB and they said fine.

I would check with the individual insurance underwriter though as they can all vary, even if it is slightly.