An interesting note on "standard pitch" may be found in the "translators notes" to the Dover edition of On the Sensation of Tone by Hermann Helmholtz. (ISBN 0-486-60753-4, 1954).
A survey of numerous organs, and of tuning forks used by various musical and standards organizations, is tabulated in about 17 pages of fine print. The frequency of the "a above middle C" (or a') from each source is given, along with details of who made each measurement. For organs, in particular, a date of manufacture of the pipes tested is generally given, allowing an easy look at how "standard pitch" may have progressed over a number of years. (Several additional pages give a reasoned analysis of the data.)
Instruments tested were produced as far back as 1361, and on through about 1880. (The original book was first published in 1885.)
The measured a' notes range from a low of 370 Hz through about 567.3.
The lists are sorted roughly in order of increasing frequency, and are divided into rough descriptive categories. Section 6 in the tabulation gives "Modern Orchestral Pitch ..." and shows values from 437 through 460.8.
A separate category for tuning forks intended to "accurately produce a' at 440 Hz" shows measured frequencies from 422.5 thru 441.3.
"Handel's own fork" dated to 1751 tested at 422.5 Hz. "Dr. Stainer's" dated to ca. 1800 showed a' at 424.6 Hz (tune your old fiddles down?) "Steinway's standard," ca 1880, was at 458.0 Hz.
Numerous "standards" have been proposed over the past few centuries, and traditional lore has it that instruments of certain periods and from particular regions may be assumed to adhere to some particular standard. The fact appears to be that, at least until electronic measurement became easy and accurate, adherence to any particular standard was more in the nature of intent than of accomplishment.
My own heresy would be to suggest that, since a free reed instrument cannot produce "linear" harmonics, the ability of the listener to "home in" on a specific pitch is extremely limited. To persons accustomed to linear instruments like pipes, strings, etc, a free reed instrument always sounds a little out of tune. We accept that as normal for the instrument. If it is actually a little out of tune, what does it matter?