Some useful info from the ‘What’s Best’ forum…
It does appear that Musashino were building the earlier ones.
"…I’d like to post my first ever Koetsu Black which I bought from an elder audiophile who in turn bought 2 units from a Hong Kong distributor Friden Marketing in the late 80s.
Having worn out the first, my friend used the second one for not very long till he decided to sell it and having heard that, I quickly snapped it amidst some other guy planning to outbid me in a dinner table gathering of audiophiles. The rule of law prevailed and I got it and marveled and savored at its beautiful sound until I decided to apply to be the country distributor of Koetsu in 2006.
Honestly I have no answer to Ki’s original posted question. Koetsu long before was company shrouded in mystery and enigma. Wooden non-sealed box, no paper tech specs, no seal, you’re lucky to get a metal of plastic cantilever/stylus protector (yes that is included always), and as I always told customers, the zen like smell of the wooden box is already half the price of what they paid for.
When I bought the Black, I was so giddy to be finally an owner of a Koetsu cartridge, as I have only heard one from a neighbor’s listening room long ago and was enamored with the sound and the mystique surrounding it. That neighbor had 2 Koetsus, Rosewood and Onyx. The Onyx was on reserve and not mounted. Not surprisingly, there were Koetsu critics, saying that highs were rolled off, bass was flabby and only the mids were worth listening to, that was in the 90s. But it didn’t deter me from buying the Black. Yes, it has the Musashino Audio mark on its top, with a serial number and here it is mounted on my ET2 arm wand.
When I became the country distributor, the Black had a new look:
It had beveled bottom corners and a slanting base near the cantilever area, and of course, it looks ‘newer’. This is part of the new generation Koetsus made by Fumihiko Sugano. If one is looking for a more vintage one, then my advise is to search for a Black that had the Musashino mark. It had the classic Koetsu sound, and it would be safe to assume that the father Sugano had a hand in the innards of the cartridge, even if the body was OEMed by another Japanese manufacture, maybe he had difficulty ‘chiseling’ metal…"