rman backup validation

version:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
Red Hat Enterprise Linux AS release 4

I found a db in an unrecoverable state this morning.  An incremental 0
ran in the wee hours while I dreamed of being in an iron man movie or
some such, but this morning I find:

RMAN> report unrecoverable;

Report of files that need backup due to unrecoverable operations
File Type of Backup Required Name
---- ----------------------- -----------------------------------
9    full or incremental     /db01/oradata/ironman/ne_adata01.dbf
11   full or incremental     /db01/oradata/ironman/tac_adata01.dbf


RMAN> restore database validate check logical;

Starting restore at 21-MAY-10 10:30:58
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=325 device type=DISK

channel ORA_DISK_1: starting validation of datafile backup set
channel ORA_DISK_1: reading from backup piece 
/var/local/database/flash_recovery_area/IRONMAN/backupset/2010_05_20/o1_mf_nnnd0_TAG20100520T200003_5zcm854r_.bkp
channel ORA_DISK_1: piece 
handle=/var/local/database/flash_recovery_area/IRONMAN/backupset/2010_05_20/o1_mf_nnnd0_TAG20100520T200003_5zcm854r_.bkp
 tag=TAG20100520T200003
channel ORA_DISK_1: restored backup piece 1
channel ORA_DISK_1: validation complete, elapsed time: 00:01:45
Finished restore at 21-MAY-10 10:32:44


Maybe "validation complete" doesn't mean all is well?
How can a level 0 with all the redo available get into a state where 
datafiles are unrecoverable?  Thanks.
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