Incorrect EST Timezone instead of EDT in Oracle
I did not investigate any further for specific database and timezone file versions, but I guess you use and old database version with an outdated timezone file.

10.2.0.5.0:

SQL&gt; select VERSION from v$timezone_file;

   VERSION
----------
         4

SQL&gt; SELECT TO_CHAR(FROM_TZ(TIMESTAMP '2020-08-01 00:00:00', 'America/New_York'),'TZD') AS TIMEZONE FROM DUAL ;

TIM
---
EDT

SQL&gt; SELECT TO_CHAR(FROM_TZ(TIMESTAMP '2021-08-01 00:00:00', 'America/New_York'),'TZD') AS TIMEZONE FROM DUAL ;

TIM
---
EST


11.2.0.4.180417:

SQL&gt; select VERSION from v$timezone_file;

   VERSION
----------
        14

SQL&gt; SELECT TO_CHAR(FROM_TZ(TIMESTAMP '2020-08-01 00:00:00', 'America/New_York'),'TZD') AS TIMEZONE FROM DUAL ;

TIM
---
EDT

SQL&gt; SELECT TO_CHAR(FROM_TZ(TIMESTAMP '2021-08-01 00:00:00', 'America/New_York'),'TZD') AS TIMEZONE FROM DUAL ;

TIM
---
EDT


It's time to upgrade.

This is a good starting point (requires a valid Oracle Support contract which you would need anyway for downloading the patch as well): Updated DST Transitions and New Time Zones in Oracle RDBMS and OJVM Time Zone File Patches (Doc ID 412160.1)