SQL Server Agent only stores a limited number of rows of history total and per job. That can be set using SSMS on the History tab of the SQL Server Agent properties or by running:

USE [msdb]

GO

EXEC msdb.dbo.sp_set_sqlagent_properties @jobhistory_max_rows=10000,

@jobhistory_max_rows_per_job=1000

GO

The default values are 1000 and 100, so you'll likely have a limited history available to you unless you changed those settings.