First pressing LPs

Different record labels have different ways to identify. Many of the record manufacturers starting from mid 70's started to put letters in circles either 'P' or 'C' P is usually for the original or the first pressing. Atlantic label for instance has on first pressings 4-digit code while 5-digit is on re-issues.

First pressings may be the best of the generics but I would suggest focusing on the imports for, generally speaking, the best sonics. Identifying first pressings is easiest with the aid of the Goldmine and Jerry Osborne's record price guide books. Pristine first pressings of desireable records usually bring the most money in the collectors market. Please understand though that collecting these types of records has little to do with audiophile playback. I find it amazing that some of the tackiest, worst music is valuable.

First of all,
No recorded source by definition can sound better than original tape.
If the original tape poorly mastered than the engineer is facing lots of trade-offs to re-master it and than release a re-issue thereafter.
All tapes are usually mastered to the artist's or producer's satisfaction. An artist or producer is not neccessarily an audiophile which is obvious in that case.
A first pressing is the one mastered from original tape that is by definition the best to the producer or artist's satisfaction but here is the BUT:...
How to produce a huge number of first-pressing records at the same time of for instance Led Zeppelin that had a high demand all over the world if there's only one original tape was produced? And the answer is that such first pressing realy was not made off an original tape as it's realy obvious. Also it's obvious that speed of mastering of mass production is high(maybe 2x or 3x).
The case with non-mass and non-commercial production is a-bit more trivial and usually has an original quality of an original tape.
For example I have both records of Tom Waits "Swordfishtrombones" and even CD!
--Original on Island 1983 vinyl. Nothing special regular flimsy and light one.
--Simply Vinyl UK reissue 2000 on 180g heavy vinyl
Original has more depth higher level and a-bit higher noise but to say good noise from the studio while reissue has everything blank and quiet. Even Tom's voice sounds thinner than on original album.

They should have sent digital tapes! What a theory! The pressings from the country of origin sound best! How can a record be noisier and sound better? Vinylites always floor me. What about all the other links in the record making chain? What if the stampers are of poor quality? What if the job of pressing is awful? What if the raw material used sucks? Does every mastering facility in the USA get a first generation master tape with which to work? So many questions, so little time...