RCD only became a requirement in the UK on 16th June 1998, so your 1978 Contessa 32 is comfortably prior to that date. Unless of course she was first "put into use" outside the EU, and has only just entered what is now called the EEA. This is though unlikely unless yours is one of those built in Canada.
Jeremy Rogers has I believe built a (very) few since 1998 and these must have a RCD category. I'd assume it would be A, but some detail might just have caught them out and made it B. That does not though mean that your boat has that category - there are lots of things more than just being the same design hull involved.