I don’t want to add to the speculation about the source of the immediate post-RL cut but suffice to say, a lot of pretty big records were made by sending copy tapes to various pressing plants simultaneously. I gather that in some cases, at least in the U.S., metal parts would be shipped. I think Atlantic relied largely on Columbia in those days for U.S. pressings; the foreign pressings would have likely come from safety/production copies that were already EQ’d--that is a reason (correct me if wrong) why you might find a ex-U.S. pressing with a Hulko or RL inscription.
I bought most of my Zep copies back when and if you can sit and listen to them in batches-- doing "shoot-outs" with eliminations, you can pretty much discern the differences over a known system. It takes time (when I did this for Zeppelin a number of years ago, these shoot outs-- which I never wrote up--were done over the course of days and weeks, and involved East and West Coast US pressing plants, UK (like the LZ I Turquoise, which I did not own) and numerous others).
You don’t need golden ears to hear the differences-- some are more dramatic than others. With LZII, I’d still put the RL at the top of the heap-- Monarch if possible and yes, there were WLPs of those which are pretty rare. I’ve heard it said that there were around 200k copies of the US RLs, which is still a decent amount of records from a collector’s standpoint, although the band was well known by the time the second LZ album was released, so that was just the "starting" runs-- from multiple plants simultaneously.
One other observation-- system character will play into how the particular pressing is perceived. I bought the MoFi LZ II when it was released, and using a Quad/Decca/subwoofer system and tubes at the time, the EQ of that cut compensated for the tonal balance of that system. I haven’t listened to that copy in a long time, but regard the vinyl compound as possibly the best- I played the hell out of some of those old MoFi (JVCs) and they are still quiet.
Among the copies of LZII here (to my memory) are multiple RLs, an early UK plum, the aforementioned 2nd JPN (which I was told was highly regarded by the Highwater Sound guy), a Canadian "TG" and probably a few others. I did have those Page supervised remasters of I-III but got rid of them when I purged before moving to Texas.
Obviously, the biggest obstacle is availability of clean players in a highly inflated market. I think I paid around $300 US to a bin diving friend for the cleanest RL and that was reasonable for both of us at the time. Today, I probably would not bother, but there are many other pressings out there, and some pretty good write-ups of them if you research. Part of the joy of this, to me, is the process of searching these out, researching, listening and comparing. It’s easier to do when a record is 50-100 bucks than 1,500 US.
Even though I have gone through quite a lot of vinyl (mainly older copies), I’ve slowed way down because of the inflated market. I will still pay for a record I want, but I’m more deliberate about it now.
There is a good thread on Hoffman about "mid-level" LZ II that also brings up a Spanish pressing (Alvear, which I have not heard) in addition to a number of others, some mentioned here.
