I'm not sure I understand what you're after. Anyhow, some comments:
- The only difference between the two files is

Code:

                                                              > update failed: YXRRSET
bar.exemple.local. 3600 IN CNAME realhost1.exemple.local.     | bar.exemple.local. 3600 IN CNAME realhost2.exemple.local.
                                                              >
                                                              > update failed: YXRRSET

, so that "update failed" is what you need to go for.

- The " OPERATION: NOERROR / FAIL:" text may be misleading, so it might be pointless to look for the string "status".

- You seem to mix up lines, records, and fields in your script. With that field separator "\n", you have a varying field count; 13/14 with OK records, 15 with error records:

Code:

NF: 15
1:  
2:  ;; ->>HEADER<<- opcode: UPDATE, status: NOERROR, id:      0
3:  ;; flags:; ZONE: 0, PREREQ: 0, UPDATE: 0, ADDITIONAL: 0
4:  ;; ZONE SECTION:
5:  ;exemple.local. IN   SOA
6:  
7:  ;; PREREQUISITE SECTION:
8:  foo.exemple.local. 0 NONE A
9:  foo.exemple.local. 0 NONE CNAME
10:  
11:  ;; UPDATE SECTION:
12:  foo.exemple.local. 3600 IN CNAME realhost1.exemple.local.
13:  
14:  update failed: YXRRSET
15:

so you might always go for field 14 or (NF-1).

- $0 will always (at least in your samples) hold "opcode", so you always split $0 into array, which will have 43 (OK records) or 46 (fails) elemants, respectively. What for?

- in your script, indentation alludes that you want to have nested ifs, but awk needs the entire branch to be enclosed in {...} if it has more than one command. So all the ifs will be executed at the same hierarchy level; the else branch will rely on an error array set way back even if the actual record is a success, and "OPERATION" wil be printed always no matter if "opcode" present in $0 or not.

Suggestion: check for the relevant fields by either
- for (i=1; i<=NF, i++) if ($i ~ "failed") print $i
or
- if (match ($0, /failed: .*$/)) print substr ($0, RSTART+7, RLENGTH-7)