ELP’s first album is one of the last pink labels before Island started using the pink rim in the UK. By the time of the pink rim, Island was pressing and distributing through EMI and the deadwax reflects EMI nomenclature. Previously, Island worked with Polygram, which used a different type of code in the dead wax. (Every once in a while you’ll find an old pink rim that used the metal parts from an earlier era-- I have a Free Tons of Sobs that bears the Polygram nomenclature even though by the time of that reissue its manufacture should have been EMI). The early pink labels are yet again different, some pressing at Orlake, with different nomenclature--Those tend to be the "bullseye" pink labels. I suppose one might find an Orlake on a slightly later pink label- after bullseye, there was the ’blocked I" in black, then the white unblocked "i," which was the last variation. These would be shown in a book like Yuri Grishin’s (if you are referring to his series on famous British labels). At the time this stuff was manufactured, it was a commodity and the average user wasn't necessarily focused on pressing plants. Even the record company executives wouldn't have paid much attention to pressing plant issues, except for business reasons; the relationship between deadwax and sonics was not even on their radar. Much of this information was unlocked by collectors years after the fact. Island was sold to Polygram and eventually merged into the Universal empire. Who knows what documentation exists for manufacture- it wasn't necessary paperwork that would have carried over through various company transfers.
And that’s just the pressing plant! Island also used a variety of mastering engineers including Sterling in the U.S. and George "Porky" Peckham, whose work (he often did the remasters in the period) was bombastic.
I generally prefer the earliest pressings on Island for sonics, e.g. Orlake over Polygram and Polygram over EMI- this is reflected in the prices as well-- The EMIs tend to sound a little hotter and brighter, the Orlakes, though a little noisier, are richer sounding. Some of the early pink labels fetch real money these days. Chris Blackwell and his crew were way ahead of the pack in signing very forward looking artists and wound up with a roster of talent that was the envy of the majors. Island essentially forced most of those labels to start signing more adventurous acts; thus, the imprints from the majors with more psych or prog sounds, e.g. Philips formed Vertigo, etc. Lots of great stuff on Island from the era.