Squeeze box (of any kind) and "subtlety is his long suit" is sort of a non-sequitor, isn't it?

It appears, from Helmholtz, that Germany used a Standard Pitch (Praetorius's suitable pitch) at A-424.2 Hz as of 1619.

"Sheibler's Pitch" was adopted at the Congress of Physicists in Stuttgart in 1834 with a "temperature corrected" pitch at A-440.2 Hz. The Wiki article that Peace linked gives some discussion about how attempts to "standardize" pitch produced some controversy of whether 440.2 or 440 should be the preferred value.

The same source shows, for "England, Scotland, and Ireland" 1803 thru 1878:

Semi-official "Standards" were:
  Hullah's              A-441.3    1842
  Society of Arts       A-444.0    1860
  Griesbachs            A-449.5    1860
  Griesbachs 2d         A-454.2    1860
  Cramer's              A-448.4    1860
  Tonic Solfa College   A-427.5    1877
  Tonic Solfa College 2 A-422.5    1877
  
  Omitting a large number of "Church Organs and Bells," 
  Concert Organs from    A-429.9 to A-454.7   (9 entries).
  Opera from             A-435.4 to A-456.1   (10 entries)
  Concerts from          A-423.7 to A-452.5   (7 entries)
  Pianofortes from       A-433.0 to A-455.9   (12 entries)
  Military Music at      A-451.9 for 2 examples.

In the US, from 1868 through at least 1880, standard pitches used by piano and organ makers were generally all above A-440, with the notable exception being Mason and Hamlin who would, on request, build to "French Pitch" at A-435.9. With that exception, the range given is from A-443.9 to A-460.8. Steinway's forks were "officially" at A-457.2 but one fork known to have been used was measured at 458.0.

The move to A-440 (or A-440.2) for physicists thus began in Germany ca. 1836. Since most of the world bought their laboratory instruments from the Germans, that pitch was in use in laboratories long before it became common as a standard for musicians.

The "international conference" in 1939 agreed that A-440 should be the standard, and that had been the value already used in laboratory measurements in most places well before then. It became "nearly universal" for physics and mathematics then or soon after.

Adoption as a true "universal standard" didn't come until the ISO action in 1955. The only real significance of the ISO Standard is that when the government ordered a flute they could now specify it's pitch by citing the standard instead of having to say "tuned to A-440." As musicians seldom write specs, or get governement funding to buy their instruments, the date has little meaning for instrument makers, who continued for some time to "offer choices" and/or to just "make what they always made."

John