Resolution:
Generally, there are below two kinds of log entries logged by the TIBCO Administrator server:

1). One which is related to the TIBCO Administrator repository, which includes the events that take place in the TIBCO Administrator repository. For example, the startup related entries of the TIBCO Administrator. These entries go into the log file defined under the tibcoadmin_<Domain_Name>.tra file under TIBCO_HOME/administrator/domain/<Domain_Name>/bin with java.property.TIBCO_APP_LOG_FILE parameter. By default, this points to the TIBCO_HOME/tra/domain/<Domain_Name>/logs/Administrator.log.
 
2). The other entries of TIBCO Administrator server are related to deployment/undeployment. These entries go to the file TIBCO_HOME/tra/domain/<Domain_Name>/logs/Administrator.log because it is internally set to this file. This can be customized using the LogFile param in the AuthorizationDomain.properties and AdministrationDomain.properties file under TIBCO_HOME/tra/domain/<Domain_Name> . This paramater has the default value of, "TIBCO_HOME/tra/domain/<Domain_Name>/logs/Administrator.log", so it is not present in the .properties file. To customize it, manually set it in the AdministrationDomain.properties and AuthorizationDomain.properties files.
 
3). By default, both paramaters are set for the TIBCO_HOME/tra/domain/<Domain_Name>/logs/Administrator.log file, so all  logs for the admin server are seen in the same file. Changing the value in the TIBCO_HOME/tra/domain/<Domain_Name>/bin/ tibcoadmin_<Domain_Name>.tra file to some other directory still creates the administrator.log file (apart from the log file defined in the  tibcoadmin_<Domain_Name>.tra file) with ZERO size because the LogFile paramaters are set internally. This file grows on deployment.

4). You can customize the log entries as per your requirements. If you want a single administrator log file you can set the parameter defined above in step 1) and step 2) to the same value.

How to customize the Administrator log file name and location.