Comment 4 for bug 520370

I think in your case using the category "Tags" better fits your needs. Have a look at the documentation:
http://rednotebook.svn.sourceforge.net/viewvc/rednotebook/trunk/doc/help.html#toc3

Categories are used for content, not for categorization. Tags however categorize entries.

You can use the Tags 1956 and 1957. They will show up automatically in the drop down list.