Ok fantastic! I deleted A00026 and did a robot inventory again. This time Netbackup got it right.
The tape is back with the correct Media ID/barcode.
Thank you all for your quick help.
For reference (vmquery output):
================================================================================
media ID: 0276L4
media type: 1/2" cartridge tape (6)
barcode: 000276L4
media description: Added by Media Manager
volume pool: ENCR_stmarytx (4)
robot type: NONE - Not Robotic (0)
volume group: ---
vault name: ---
vault sent date: ---
vault return date: ---
vault slot: ---
vault session id: ---
vault container id: -
created: Fri 21 Dec 2012 08:29:34 AM CST
assigned: Sat 16 Feb 2013 07:22:55 AM CST
last mounted: Tue 19 Feb 2013 06:03:08 AM CST
first mount: Sun 30 Dec 2012 03:37:25 AM CST
expiration date: ---
number of mounts: 5
max mounts allowed: ---
status: 0x0
================================================================================