Holdings gaps
[L=1955,5,33,41; 1956,21,22; 1957, 1; 1959,6,10,17,18,23,24,31; 1961,2,3,18,26,32,38; 1962,23,48; 1964,48,50f; 1965,12,27; 1966,37; 1967,10; 1968,4; 1969,17; 1970,12,28-31,38; 1971,26; 1972,3-5,13-27; 1973,2,20,31; 1974,7-8,25,45; 1975,41-46;1976,6,10,22; 1977,8,17ff; 1979,28,43,45,49; 1980,1-10,12,14-52; 1981,1-25; 1982,10,46; 1990,4,21,23-26; 1991,18,22,45,48; 1993,12,14-[?]]