older LPs - different EQ?

After seeing 35,000+ LPs in one place on Sunday, including a wide variety of selections from the early years of recorded music, I suddenly remembered a foggy thing that I read a while back, and I want to confirm.

My impression is that pre-1958 or so (1955?) the record companies used a different equalization curve than the now-ubiquitous RIAA equalization. Is this true? If so, what sort of phono stages do equalization for these properly? Anything else to be aware of in this space?
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Hmm... where would one find out which labels require which curves? I did play one of those old LPs and it did sound weird, but the equipment was laughably unrealistic, badly configured (bass, treble whacked max, loudness turned on, big boomy Kmart speakers). I wasn't 100% sure that I was hearing a weird EQ curve or just bad reproduction. (The equipment was quite good enough, though to figure out if the LPs were in good shape, which is what I think is its intent.)
You'll be in for a surprise.
Most labels used their "own" cutting curve until 1958 - and even in 1964 the RIAA had to issue a reminder to the record producers that in fact they had agreed to use the RIAA curve and would all please use this from now on...

While they confirm they have not all curves ever used FM ACOUSTICS has researched curves of 85 different labels so far - all of which can be correctly reproduced with these phono preamps.

Once you hear the difference when the correct setting is used in comparison with the RIAA setting you will not want to listen again without correct curves. The difference can be larger than the differences in hifi systems.
chiefslave1: which phono preamps do this? Looking at the FM Acoustics web site shows two phono stages, but neither of them seem to claim anything about various equalization curves. Am I looking in the right place?