Question for Guide-y peeps ...

Just looked at the Girlguiding UK website ('cos of Xanthe's(or maybe even Rosie's) post) and saw a badge declaring it to be Brownies 90th year. Now I'm sure I went to a 60th celebration when I was a Brownie, but it would have had to be in 1970 or 71, which is blatantly more than 30 years ago *puzzled* ?