Holdings gaps
[N=1958-1961; 1962.1-4,6-12; 1963; 1964.1-10,12; 1965.1-5,8,10-12; 1966; 1967.1-6,8-11; 1968.1-5,7-12; 1969.1-2,5-12; 1970.1-4,6,8-11; 1971.1-3,5-6,8-9,12; 1972.1-8,10-12; 1973.1,3-12; 1974.1-4,6-12; 1975; 1976; 1977.1-7,9-10,12; 1978 - 1980; 2010,10; 2016,6]