They're just from different regions, though you can't get the ota's from other countries. You can use any one
There is nothing official, because LG don't provide any real form of Changelogs - particularly where bugs are concerned.
For the d802 OPEN versions, the 4 builds are
something like this:
20A - very buggy and replaced quickly by 20B - Forget it. We have.
20B - left hand channel audio problems on SOME hardware.
20C - audio problems gone
20A, 20B, 20C - "Bluetooth using battery" reporting error present.
20D - Knock code added and "Bluetooth using battery" reporting fixed. Battery drain increased from 20C.
There may be other funnies, of course.
Every Open EUR version is binary identical to the others (GB/ES/PT/DE etc.)
Personally, I use 20C on the Stock phone as it is the "least problematic". That doesn't mean it is so for everyone and every phone hardware version.
Also note that these are MY observations only. I have built the flashable versions of all the above (except the flaky 20A) as found in the 802 development forum.