Its all b****cks, if they are on the ball they'll chase you. I was with a broker and I had 2 cars on there, it was really unclear which car had what no claims etc....(there are 2 drivers and cars have been on there a while at different times etc)
I changed insurer and all of a sudden I didn't have as many as I thought. I then had to pay an extra £90 to the new insurer as they quote was then wrong as the number of year was wrong.
Personally I think NCB should be calculated on the driver not the individual cars. The other thing that narks me is if you have an accident and it was not your fault (I had someone go up my backside oh er, back in 02) it stays on there for a while and I'm sure I have been penalised.....