I believe Rob didn't bother writing it out, but to be exact he would have written
so if playing the 1891/1924/1957/1990 season - only 1892/1925/1958/1991, 1893/1926/1959/1992, 1894/1927/1960/1993 picks can be traded - as well as during the 1892/1925/1958/1991 draft, only the 1892/1925/1958/1991, 1892/1925/1958/1991 picks may be traded - once that draft is over - then it rolls over to the next 3 seaons - HOWEVER - no trading during the inaugural draft.
ALL players from the seasons being simmed will be put in a common pool - so, in the inaugural draft, all player from 1895, 1918, 1951, and 1984 are available to be drafted at all times (assuming they haven't already been drafted by somebody else already.)