Hi John,
APO 96555 is still open according to information in the lastest DOD Acctivity Address Directory. The DODAAC does show the missle range address as deleted in 1998. There are 26 addresses in the DODAAC for this APO, some with effective dates of 2000 / 2001. URL for a searchable database: http://daynt6c.daas.dla.mil/dodaac/zip.htm

Paul