... I stand by what I said in my review of a Oistrakh Heliodor... that the older and less sophisticated recordings don't stand up as well to the "stereo-isation" of original mono recordings...
(The problem with the Oistrakh is that as lead instrument, the process doesn't really get a handle on which side to favour his violin at any given moment, which is a little distracting, as the "stereo" sounds like an old recording in a schizophrenic state, and doesn't hang together too well)
...but this is very good, and I can't, in all honesty tell if it is an original stereo, or a processed mono to stereo (I suspect the latter, but the ear doesn't hear it).
And all Heliodors follow the german (DG) pressing fashion of having the patent date stamped in the deadwax, in case you come across the odd one like my oistrakh, which doesn't have the date on the cover or labels.
Release date September 1968 from Heliodor ad in that month's edition of GRAMOPHONE. I'll have to switch to my tablet in a minute in order to get a copy of the ad, it's not possible to copy it from my laptop.
I'm going to have to give this a spin, as it has the unusual property of not having the word: "Transcription" under the "stereo" on the labels, where the other Heliodors I have do...
(Although this does have it on the back cover)
...It just makes me wonder if this might signify a direct stereo reproduction of an original stereo recording (where they existed in the first instance), as opposed to the others, which seem to me to be manufactured (artificial) stereo effect from the original mono recordings made before stereo was available.
If this is the case, there might be a few little gems among the Heliodors signified by the absence of the word "Transcription" under stereo... and it might offer a way to get early stereo Deutsche Grammophon recordings very cheaply.
(I don't hold my breath though... will report back later if this is the case :)