A.S. stands for Anno Societatis -- "in the year of our Society." The chart below shows how years in the Society match up to years in modern reckoning, with the numbers of Pennsic Wars thrown in for good measure:

May 1 of      through April 30 of A.S. Pennsic War (August)
1966 1967 I (1)
1967 1968 II (2)
1968 1969 III (3)
1969 1970 IV (4)
1970 1971 V (5)
1971 1972 VI (6)
1972 1973 VII (7) --1
1973 1974 VIII (8) -- 2
1974 1975 IX (9) -- 3
1975 1976 X (10) -- 4
1976 1977 XI (11) -- 5
1977 1978 XII (12) -- 6
1978 1979 XIII (13) -- 7
1979 1980 XIV (14) -- 8
1980 1981 XV (15) -- 9
1981 1982 XVI (16) -- 10
1982 1983 XVII (17) -- 11
1983 1984 XVIII (18) -- 12
1984 1985 XIX (19) -- 13
1985 1986 XX (20) -- 14
1986 1987 XXI (21) -- 15
1987 1988 XXII (22) -- 16
1988 1989 XXIII (23) -- 17
1989 1990 XXIV (24) -- 18
1990 1991 XXV (25) -- 19
1991 1992 XXVI (26) -- 20
1992 1993 XXVII (27) -- 21
1993 1994 XXVIII (28) -- 22
1994 1995 XXIX (29) -- 23
1995 1996 XXX (30) -- 24
1996 1997 XXXI (31) -- 25
1997 1998 XXXII (32) -- 26
1998 1999 XXXIII (33) -- 27
1999 2000 XXXIV (34) -- 28
2000 2001 XXXV (35) -- 29
2001 2002 XXXVI (36) -- 30
2002 2003 XXXVII (37) -- 31
2003 2004 XXXVIII (38) -- 32
2004 2005 XXXIX (39) -- 33
2005 2006 XL (40) -- 34
2006 2007 XLI (41) -- 35
2007 2008 XLII (42) -- 36
2008 2009 XLIII (43) -- 37
2009 2010 XLIV (44) -- 38
2010 2011 XLV (45) -- 39
2011 2012 XLVI (46) -- 40
2012 2013 XLVII (47) -- 41
2013 2014 XLVIII (48) -- 42
2014 2015 XLIX (49) -- 43
2015 2016 L (50) -- 44
2016 2017 LI (51) -- 45
2017 2018 LII (52) -- 46
2018 2019 LIII (53) -- 47
2019 2020 LIV (54) -- 48
2020 2021 LV (55) -- Pennsic Cancelled
2021 2022 LV (56) -- Pennsic Cancelled
2022 2023 LV (57) -- 49
2023 2024 LV (58) -- 50