Hi Mary
For the Tornado Class, Greg Scace tells me that officially the number is assigned to the boat and should transfer with the boat. However, the recent trend has been for the the sailor to keep their number when they sell and replace their boat with another T. So... Johnny, Lars and Robbie have had the same sail number for 12 years even though they have had several boats over the years. It's a lot of effort to keep track of boats, measurment certificates etc etc. The T Class is supposed to build a database of measurment certificates for each boat on line but it is taking some time to implement and its not clear if the club sailors will join in and get measured and registered.
It's a lot of work.
Take Care
Mark