Just left the scheme myself in june, Directline was alot more money, as was adamiral or lv, than a few of the quotes I had via a comparison site (all like for like) one of which we already have home insurance with and got a discount for that also, so went with them. Definitely worth shopping around.
They also accepted the letter i got from rsa (which you get after you leave the scheme) infact all i ones i did contact said they accepted the rsa letter as proof of ncb.
When the policy came threw, as i wanted physical documents, it said my claims history had been checked and verified and no proof was needed to be sent to them.
I had been on the scheme for 11+ years but the claim history only goes back 9 years.
As macca says if you can list both do so, if you cannot best to call them, I did as for some reason my private plate was not coming back, but it was a new car, I bought so i had to call them and i actually then paid less than the online quote even though i gave them the ref number of the quote over the phone.
Only problem i can maybe see you having is if you was not the main driver or holder of any policy, over the last 9 years.