So, I created a new category (DLRERA, with decades as subcategories) and also created new terms for 1950s Cast Members, 1960s Cast Members, 1970s Cast Members, 1980s Cast Members, 1990s Cast Members, and 2000s Cast Members. While the Cast Member terms denote something specific, the DLRERA category is a little more ambiguous. I have a working definition that a a decade should be applied to a term if it had some presence in or influence on the Disneyland Resort during that time. A Cast Member who worked at the Park in the 1970s would have the 1970s category applied, obviously. I worked at Disneyland in the 2000s, but I've also applied 1990s to myself because I was active in the Usenet community, had a popular Disneyland web site, co-founded the Bruce Gordon Fan Club, etc., etc. The categories are sort of a way of pulling all the terms for a particular decade together.
I have not gone through to apply this categorization to every term in the thesaurus just yet (and frankly, I'm not sure I'd go to the trouble of categorizing all of the date terms themselves). The process of back-categorizing thousands and thousands of Cast Members was onerous enough, as I had to read the notes I'd typed about them to determine when they worked. These are the numbers I have so far, with overlap between categories possible and occurring:
1950s Cast Members: 628The numbers reflect the sources I've used thus far and so shouldn't be used for statistical purposes. The number of 1970s Cast Members, in particular, reflects the large number of Disneyland Lines from early in that decade.
1960s Cast Members: 1,203
1970s Cast Members: 2,111
1980s Cast Members: 1,096
1990s Cast Members: 1,240
2000s Cast Members: 2,779