Do we know if the early commercial electrics by Victor and HMV used any equalization? Since there was no commercial record player on the home market that used an amplifier until November, 1925, there’s an April-October or later period where there is no means of introducing a circuit that inverts any electronic change from what reached the cutting head.
The record companies would not abandon the record market which used the acoustic playback process for half a year or create a product that sounded poor on the installed base of home players. Yes the acoustic Orthophonics were available by then but few could afford them.
If this is so, such 78s should be played back flat.
Any hard data on this question?