The Royal Yachting Association in the UK runs a similar Portsmouth scheme but does not publish ratings for little-used classes unless they have had a certain number of returns over some time period. They drop off the current list and the scorer must refer to older lists to get a rating for older boats etc.

I don't know the details but it may be worth talking to them? See http://www.rya.org.uk/Technical/yardstick/. The RYA categorise ratings into Primary, Secondary, MoreReturnsRequired and Recorded; giving the user of the scheme some idea about the confidence the RYA have in published numbers; while also encouraging some classes to send in more returns.

Regards,
Colin J
www.sailwave.com