Japan Mint started to use these marks in 1979.
The following (constantly updated) table includes all currently known time coordinates for these marks.
AC - June 28, 1979
AB - November 28, 1979
BA - February 27, 1980
AJ - April 26, 1980
BB - April 26, 1980
AL - April 29, 1980
AL - May 28, 1980
BB - May 28, 1980
BC - May 28, 1980
BB - July 30, 1980
BG - September 27, 1980
BH - August 27, 1980
AK - November 3, 1980
CA - February 28, 1981
BK - February 28, 1981
CA - March 28, 1981
BA - April 29, 1981
BF - April 29, 1981
CA - April 29, 1981
CC - June 27, 1981
СD - July 29, 1981
CF - September 30, 1981
CF - October 31, 1981
AH - November 3, 1981
CB - November 3, 1981
CC - November 3, 1981
CI - November 29, 1981
CI - December 26, 1981
CJ - February 27, 1982
CB - April 29, 1982
CC - September 25, 1982
DA - November 3, 1982
DE - April 25, 1983
DL - April 29, 1983
DE - July 15, 1983
EB - April 29, 1984
FB - November 3, 1984
FG - November 3, 1984
DC - December 26, 1984
EК - April 29, 1985
FA - November 3, 1985
FF - November 3, 1985
CK - December 28, 1985
GH - April 29, 1986
DB - June 25, 1986
CL - August 27, 1986
CL - October 29, 1986
FE - November 3, 1986
GI - November 3, 1986
GK - November 3, 1986
HJ - November 3, 1987
IF - April 29, 1988
IK - April 29, 1988
CI - July 30, 1988
CK - October 29, 1988
DA - October 29, 1988
JF - November 1988
CH - February 24, 1989
JJ - April 29, 1989
CH - May 31, 1989
CL - September 30, 1989
KG - October 29, 1989
JJ - November 3, 1989
KD - November 3, 1989
DB - February 24, 1990
KK - April 29, 1990
DA - July 28, 1990
DB - September 28, 1990
KZ - November 3, 1990
LB - November 3, 1990
LH - April 29, 1991
LK - April 29, 1991
LH - October 30, 1991
MC - November 3, 1991
MF - November 3, 1991
JL - November 15, 1991
KG - November 15, 1991
MJ - April 29, 1992
MK - April 29, 1992
NE - September 30, 1992
NL - April 29, 1993
OG - May 29, 1993
QE - September 25, 1993
OF - December 22, 1993
OG - January 29, 1994
OI - April 29, 1994
PG - November 3, 1994
OA - April 29, 1995
OG - September 30, 1995
OE - November 3, 1995
OI - April 29, 1996
PJ - September 28, 1996
RH - November 3, 1996
RR - November 3, 1996
SG - November 3, 1997
SG- April 29, 1998
SL - November 3, 1998
TA - November 3, 1998
SH - November 31, 1998
SI - November 31, 1998
TL - April 29, 1999
IK - August 25, 1999
UK - April 29, 2000
VC - July 29, 2000
WJ - April 29, 2002
XD - November 3, 2002
XG - November 3, 2002
VC - December 25, 2002
YG - November 3, 2003
YH - November 3, 2003
YL- November 3, 2003
ZA - April 29, 2004
ZB - April 29, 2004
J5 - August 9, 2004
ZС - November 3, 2004
ZJ - April 29, 2005
A5 - November 3, 2005
AZ - November 3, 2006
BZ - March 18, 2007
C3 - November 3, 2007
CX - March 29, 2008
CX - April 29, 2008
D8 - October 29, 2008
D7 - November 3, 2008
D8 - May 30, 2009
DZ - November 3, 2009
EY - April 29, 2010
F9 - April 29, 2011
I5 - March 3, 2013
IY- January 29, 2014
K5 - October 31, 2015
K7 - January 30, 2016
L2 - August 25, 2016
M2 - April 29, 2017
Q1 - June 30, 2021
The following (constantly updated) table includes all currently known time coordinates for these marks.
AC - June 28, 1979
AB - November 28, 1979
BA - February 27, 1980
AJ - April 26, 1980
BB - April 26, 1980
AL - April 29, 1980
AL - May 28, 1980
BB - May 28, 1980
BC - May 28, 1980
BB - July 30, 1980
BG - September 27, 1980
BH - August 27, 1980
AK - November 3, 1980
CA - February 28, 1981
BK - February 28, 1981
CA - March 28, 1981
BA - April 29, 1981
BF - April 29, 1981
CA - April 29, 1981
CC - June 27, 1981
СD - July 29, 1981
CF - September 30, 1981
CF - October 31, 1981
AH - November 3, 1981
CB - November 3, 1981
CC - November 3, 1981
CI - November 29, 1981
CI - December 26, 1981
CJ - February 27, 1982
CB - April 29, 1982
CC - September 25, 1982
DA - November 3, 1982
DE - April 25, 1983
DL - April 29, 1983
DE - July 15, 1983
EB - April 29, 1984
FB - November 3, 1984
FG - November 3, 1984
DC - December 26, 1984
EК - April 29, 1985
FA - November 3, 1985
FF - November 3, 1985
CK - December 28, 1985
GH - April 29, 1986
DB - June 25, 1986
CL - August 27, 1986
CL - October 29, 1986
FE - November 3, 1986
GI - November 3, 1986
GK - November 3, 1986
HJ - November 3, 1987
IF - April 29, 1988
IK - April 29, 1988
CI - July 30, 1988
CK - October 29, 1988
DA - October 29, 1988
JF - November 1988
CH - February 24, 1989
JJ - April 29, 1989
CH - May 31, 1989
CL - September 30, 1989
KG - October 29, 1989
JJ - November 3, 1989
KD - November 3, 1989
DB - February 24, 1990
KK - April 29, 1990
DA - July 28, 1990
DB - September 28, 1990
KZ - November 3, 1990
LB - November 3, 1990
LH - April 29, 1991
LK - April 29, 1991
LH - October 30, 1991
MC - November 3, 1991
MF - November 3, 1991
JL - November 15, 1991
KG - November 15, 1991
MJ - April 29, 1992
MK - April 29, 1992
NE - September 30, 1992
NL - April 29, 1993
OG - May 29, 1993
QE - September 25, 1993
OF - December 22, 1993
OG - January 29, 1994
OI - April 29, 1994
PG - November 3, 1994
OA - April 29, 1995
OG - September 30, 1995
OE - November 3, 1995
OI - April 29, 1996
PJ - September 28, 1996
RH - November 3, 1996
RR - November 3, 1996
SG - November 3, 1997
SG- April 29, 1998
SL - November 3, 1998
TA - November 3, 1998
SH - November 31, 1998
SI - November 31, 1998
TL - April 29, 1999
IK - August 25, 1999
UK - April 29, 2000
VC - July 29, 2000
WJ - April 29, 2002
XD - November 3, 2002
XG - November 3, 2002
VC - December 25, 2002
YG - November 3, 2003
YH - November 3, 2003
YL- November 3, 2003
ZA - April 29, 2004
ZB - April 29, 2004
J5 - August 9, 2004
ZС - November 3, 2004
ZJ - April 29, 2005
A5 - November 3, 2005
AZ - November 3, 2006
BZ - March 18, 2007
C3 - November 3, 2007
CX - March 29, 2008
CX - April 29, 2008
D8 - October 29, 2008
D7 - November 3, 2008
D8 - May 30, 2009
DZ - November 3, 2009
EY - April 29, 2010
F9 - April 29, 2011
I5 - March 3, 2013
IY- January 29, 2014
K5 - October 31, 2015
K7 - January 30, 2016
L2 - August 25, 2016
M2 - April 29, 2017
Q1 - June 30, 2021