Helmholtz reported 203 different accurately measured Standard Pitches used in Europe, in his "Corrected 4th edition" published in 1877, and "Translator's Additions" in the English translation of that edition of his book book added about 40 additional ones to bring the data up to 1885. There have been numerous others since.

In Helmholtz's list, "Standard A" values ranged from 370 Hz to 505.8 Hz, Translator's additions extended the range to 567.3 Hz as there had been an upward creeping of the standards/pitches used by Orchestras in the period from around 1850 to 1885. This trend wobbled along for about another century, both up and down.

In much of the first half of the 20th century, the "scientific definition" of pitch was based on a middle C of 256 Hz, which gave an A of about 430 Hz, and many "piano tuners" continued to use that "Standard Pitch" until ca 1960 on "student home pianos" where the piano wasn't in prime shape, may have been built to standards that anticipated the lower pitch, and the lower tension let a piano in less than perfect condition stay in tune a little longer. (They hardly ever stay in good tune when the soundboard breaks.)

When the New (Scientific) Standard Pitch at A440 began to be fairly widely used (especially by instrument makers), the custom was to call it the "Concert Pitch" to distinguish between the A440 and the C256 (~A430) that continued (colloquially) to be called "Standard Pitch" for a very long time (by those who knew that there was a difference).

Most small bands/combos now tune approximately to "Concert Pitch" because that's where their instruments are built to be. Most stringed instruments can be tuned pretty much "anywhere" but the majority of wind instruments have a fairly limited range of tuning.

In orchestral playing though, the "A" is whatever the concertmaster plays when it's time to tune up. The "pitch" to be used may be selected by the conductor, who is an absolute dictator (often with appropriate personality). In some cases it's pretty much a matter of where the concertmaster quit tuning backstage before the orchestra sat down.

We (an anonymous small group of nerds with musical background) confirmed that the "Boston Pops" in the early 1960s did in fact tune around 1.5 semitones higher than the "Boston Symphony" – because that's the way the Conductor liked it. Before electronic tuners were cheap, determining an exact pitch of either was difficult enough that we never bothered. Documentation by others with better instrumentation in that particular era did report "normal tunings" used by various orchestras, and they covered a wider than expected range, although I don't recall any that were more than about one full tone "off A440").

Now with a couple of hundred different absolute tunings, attempting to "achieve absolute perfect" pitch becomes something of a puzzle of which one to adopt as your own personal calibration.

My observation of a couple of individuals who claimed "perfect pitch" was that they generally picked the same note name when the same key was hit, on different pianos that were, in fact, tuned differently. Once they heard any two notes in a recognizable interval, they might have a sufficiently "fixed feeling" for what scale the notes would be in if both pianos were "close to being in tune to a conventionally used pitch" but once they'd "zeroed" on the scale of a given instrument they actually were using a well developed sense of relative pitch rather than any absolute thing.

Relative pitch sense is, IMO, a much more useful ability than fussing about the absolute. You develop that sense by noting that most "tunes" are accented on notes that – taken consecutively – form a "standard interval," and some intervals are more common than others "because they sound nicer." You may need to practice lots of "scale exercises" that run intervals as well as just running up and down the scale.

It's no harder than finding you've got a grizzly bear in your bedroom and becoming familiar enough to keep the bear happy. (Instruction might be the equivalent of keeping the bear well fed, and often helps.)

John