its usually down to each insurance company. the one you are presently (or were most recently) with will give you details. most work on a maximum of 5, but if you have more, they will tell you. ncd is not an official thing, more of a gentlemans agreement if you like, that insurances use to entice customers. my ncd is protected, but when i claimed, no other insurance companies will protect it now, only the one i'm with. remember, ncd only lasts 2 years from a policy running out.