Obviously, all counts will be somewhat inaccurate because registration figures are not updated the instant a car is totalled. However, any sub two-year interval is guaranteed to be more inaccurate than a two-year or greater interval: with a sub two-year interval, count #2 may still have some of the cars erroneously registered at count#1 whereas it will definitely not if if they are two years or more apart. And since counts are decreasing, the error associated with count #1 will be larger than the error associated with count #2.

If we do a count now, we will get cars that were actually totalled before the last count and still registered.