Database Software

This occiurs on a ebusiness suite database.
we were doing production upgrade of a 12.0.4 instance to 12.1.1 . we had to take hot backup of db after 12.1.1

We were doing rman backup and had following issue : input archived log thread=2 sequence=9795 RECID=19526 STAMP=766948258
input archived log thread=2 sequence=9796 RECID=19528 STAMP=766951128
channel diskchannel: starting piece 1 at 11-NOV-11
released channel: diskchannel
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of backup command on diskchannel channel at 11/11/2011 17:58:52
ORA-19809: limit exceeded for recovery files
ORA-19804: cannot reclaim 54436310016 bytes disk space from 107374182400 limit
Recovery Manager complete.
select name
, floor(space_limit / 1024 / 1024 /1024) "Size GB"
, ceil(space_used / 1024 / 1024/1024) "Used GB"
from v$recovery_file_dest
order by name
;]

gave 100G usage and 100G allocated for FRA area

we fixed it by doing crosscheck of arch logs and deleting obsolete arch logs. I understood this.
we resumed applying 12.1.3 patch on top of the instance
But while running adpatch, i kept monitoring usage of FRA using same sql and at one point, the space_used was same as space_allocated

The sql used was :
select name
, floor(space_limit / 1024 / 1024 /1024) "Size GB"
, ceil(space_used / 1024 / 1024/1024) "Used GB"
from v$recovery_file_dest
order by name

However adpatch did not fail and there was no information in alert log also

Can u pl tell me why adpatch didnt fail and why alert log didnt complain when the space_used was 100GB in above query