No, you're correct, not in 1950. In the pre-hifi era, every record label had their own playback curve, although by 1950, many of them were moving towards a flat response. Calibration to a flat response became universal with the RIAA standards in the early hifi era... around 1954.
Bad recordings don't mean that there weren't standards. Thhankfully, today, CDs are remarkably consistent, at least with classical and jazz. Contemporary rock music can be all over the place, but that's because so much work is being done in home studios now. I have my system calibrated to a flat response and there are only a few recordings I need to reach for the tone controls to correct... and all of those are from the pre-hifi era and are very rough transfers from shellac and amateur recordings. (early be bop)
Most people don't understand what calibrating to a flat response means, because although it is taken for granted in professional studios, few home audio enthusiasts go to the trouble of calibrating their systems. It's the best thing you can do for sound quality though. Balanced response is clearer, more transparent, more focused and makes all professionally recorded music sound better.
Calibration to a flat response may have become universal in 1954, but that doesn't mean it was always used. Before bands got famous, they didn't record their albums in "hi-end" studios, and the results are terrible. This is true for a vast vast majority of bands, not just in pop or early be bop music but in: rock, pop, blues, alot of small jazz ensembles, funk, soul, rnb, metal etc etc etc from the 1950s all the way to the end of the 70s, 15 years AFTER that "standard". And I'm not talking about unknown little bands noone's heard of either. There are an incredible number of albums that were recorded on a 2 track set in the middle of the room while the musicians all bunched up together and played - and on a recording like that, even the best engineers had a hard time doing something good (if they even tried, which didn't happen for many artists).
Today, yes, CDs are consistent, but the vast majority of my music collection goes from the 1920s to the 1980s. So the problem is still there as far as I'm concerned. Thankfully, some remasters squeezed out as much as they could from the terrible recordings, but compared to a modern "standard" release, they are still far from being good.
That being said you did get me curious enough to try to calibrate my system to a flat response and see what the fuss is about. I'll be trying it in the future, even if I have my doubts as to whether or not I'll enjoy it more than just adding my tube amp in the mix.