The spin values of each isotope of carbon are given on wiki here. When showing nuclear spin values the notation (1/2+)# is used. I dont understand what the () brackets and # hashtag are for? At the bottom of the page, they clarify it by saying: "Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses." Are these values not specifically calculated from first principles or do we depend on "systematic trends" to predict them?