One way of homing in on pitch is to determine at what pitch the piano was tuned.
Years ago I spoke to the tuner at Steinway who did the pianos in the Victor Studio in Carnegie Hall in the early 1920s. He worked to A=440.
I realize I'm making some broad assumptions here regarding studio instrument maintenance for other companies, but there may be anecdotal evidence from performer interviews that can be useful in this regard.
From: Association for Recorded Sound Discussion List [mailto:[log in to unmask]] On Behalf Of Jolyon S Hudson
Sent: Friday, November 27, 2015 10:46 AM
To: [log in to unmask]
Subject: Re: [ARSCLIST] 78rpm replay speeds & pitch
Ah but 78 is 78
The two speed 78.26 rpm and 77.92 rpm are dependent on the strobe being calculated on 60Hz or 50Hz frequency. I would just stick to the pitch and forget the speed altogether as there are too many variables – too much drain on the supply will drop the frequency in any case, lots of such arcana to contend with.
Not that you can be sure that it was A=440hz, it may have been 435 or 443 or just about anything on the day of recording.
Best thing is to stick to a frequency typical of the time and place of the recording.
If you don't know what that was – I mean who does know – I would first try it at A=440Hz and see what it sounds like. Maybe ask a few other people to have a listen as you might have to lower the pitch a bit, even the opposite and make it a bit sharper. After a while you may get to feel your way around the problem through listening.
Just remember 78 an expression of hope rather than a statement of fact.