Holdings gaps
[N=1975,7u.9; 1976,2u.4-8u.10-12; 1977,7; 1981,11; 1985,3u.5-12; 1986,1-8u.10-12; 1987,1u.4-5u.7; 1988,6u.8u.12; 1989,1u.3u.8u.12; 1990,1-2u.4-7u.11-12; 1991,1-2u.12; 1992,1u.4-8u.12; 1993,4; 1994,7; 1995,1u.3u.9; 1996,3-4u.11; 1997,5; 1998,5; 2000,8; 2001,2; 2014,5]