well well... Let it be known, older CWM backups do work with current CWM5
Last night i pretty much did what you are now suggesting...
1. Used smartflash to load "bin_lgp990at-00-v20l-eur-xx-oct-20-2011+0(1)"
2. Rooted the phone with "UnlockRoot v2.3.1"
3. Downloaded Rom Manager - Installed ClockworkMod V22.214.171.124
4. Created a backup with ClockworkMod - (its faster than smartflash)
5. Used Rom manager to load older bakcup (my old stock one)
6. 10 mins later CWM recovery finished loading the old backup
7. Rebooted and phone didnt go past LG logo, so it was bricked again..
After you posted, i said.. lets do it again why not, worst it can happen is that it gets bricked again lol.. no biggie.. i had a little bit of time to kill
Well, what do you know.. this time it worked!!
But I'm baffled as to why it didn't work last night with same steps and files..
I believe if you do things following the same steps you should get the same results... i guess i was wrong