Display all accounts

I have 3 tables
CREATE TABLE [dbo].[ACCT_MASTER](
[POLICY_YEAR] [char](4) NULL,
[GL_ACCOUNT] [nvarchar](8) NULL,
[GL_ACCT_DESCRIPTION] [nvarchar](100) NULL,
[GL_ACCT_LINE_NUM] [int] NULL,
[GL_NUM_LINE_NUM] [int] NULL,
[GENERAL] [int] NULL,
[ACTIVE] [int] NULL
)
CREATE TABLE [dbo].[HISTORY](

[ACCT_PERIOD] [nvarchar](4) NOT NULL,
[GL_NUMBER] [nvarchar](13) NOT NULL,
[TRAN_DATE] [smalldatetime] NOT NULL,
[DESC_LINE] [nvarchar](2000) NULL,
[TRAN_TYPE] [char](1) NULL,
[AMOUNT] [money] NULL
)
CREATE TABLE [dbo].[DATES](
[GL_CUR_EOM_DATE] [smalldatetime] NOT NULL,
[GL_PRIOR_EOM_DATE] [smalldatetime] NOT NULL,
[GL_CUR_ACCTG_PERIOD] [nvarchar](4) NOT NULL,
[GL_PRIOR_ACCTG_PERIOD] [nvarchar](4) NOT NULL

)


ACCT_MASTER HISTORY Dates
Gl_ACCOUNT year GL_NUMBER Perid
12345-00 2013 12345-00-2013 1304
67890-00 2010 67890-00-2010 1305
54321-08 2013 54321-00-2013 1304
.
.
Total of 3640 accounts
I can’t figure out how to display all 3640 accounts. If there is no match in HISTORY table for this period display 0 for the calculations but display Gl_ACCOUNT + year.
12345-00-2013
67890-00-2010 0
54321-00-2013
All 3640 rows here

My code shows only 3469 records.
select M.GL_ACCOUNT +'-'+ isnull(policy_year, '0000')NewGL, isNull (SUM(PRIOR_VDIFFPRIOR), 0)as [PriorEndOfMont],
ISNULL(sum(CURR_VDIFFPRIOR),0) as [CurrentEndOfmonth] ,
isnull (SUM (PRIOR_VDIFFPRIOR),0) - isnull (sum(CURR_VDIFFPRIOR),0) as Diffrence
from GL_ACCT_MASTER m
left outer join SUMMARY s on M.GL_ACCOUNT +'-'+ isnull(policy_year, '0000') = s.GL_NUMBER
group by GL_NUMBER,M.GL_ACCOUNT +'-'+ isnull(policy_year, '0000')order by GL_NUMBER,M.GL_ACCOUNT +'-'+ isnull(policy_year, '0000')