A comment from my days as a novice piano tuner / collector of old band instruments...
The "standard of pitch" has been a floating "standard" for centuries, depending on geographic region / musical tastes...
The present "standard of pitch" ( A above middle C = 440hz ) was not officially recognized until 1939 or 1940.
Prior to that, "A" was usually fixed at 435hz, often known as "Low Pitch" or LP.
This was to distinguish wind / other fixed-pitch instruments from the "High-Pitch" variety of the late 19th / early 20th century, where "A" = 456hz.
This fad is usually attributed to the French, looking for a "brighter" sound from their bands and orchestras. "High-Pitch" instruments were generally abandoned by WW I; they still turn up in attics, antique shops, etc.
Going back further, in Mozart and Bach's times, the standard of pitch was usually lower, with "A" hovering somewhere around 415hz. This would vary from country to country, or region to region.
This "floating" pitch standard still exists; there are rumors of Italian orchestras starting to push tuning above 440hz, and I personally had an experience several years ago when a Tango show played my performing arts center, and well had to pull the house piano up to A=442hz

, to match the four Bandoneons that were in the tango orchestra...
So, all that said, if you're going to try to set the speed of a DD player to the "A" on a demo record, it was probably for the A=435hz "Low Pitch". Setting your machine to present A=440hz would probably have it running a tad fast.
I use a 78 rpm stroboscopic disc and set it just fast enough that lines begin to "walk" slowly ( in whichever direction "faster" is).
Either that, or I slip a bit of paper under the edge of the disc and count revs / minute...
Has anyone ever made-up an 80 RPM strobe disc ?