No idea on the serial numbers.  However, I'm pretty sure that all the Matrix 1000s were made in Japan by Hammond Suzuki, including the pre-Gibson ones.  I doubt there is any difference in quality.
By the mid '80s Oberheim was looking to cut production costs in order to compete with the Japanese synth manufacturers.  Later DX drum machines (DXa), the Matrix-6 and -6R, Matrix 1000, Prommer, Xk, DPX-1, and later designs were all designed and distributed in the US by Oberheim, but manufactured by Hammond Suzuki in Japan.

-- Paul White

At 02:12 PM 4/23/09, you wrote:

Thanks, Paul, for that good info.
It makes me wonder what might be the general serial number range
for the Matrix-1000s produced by Oberheim. Any guesses
I'm just wondering because If and when I buy a Matrix-1000 again, I want it to be one of the ones made by Oberheim, not Gibson.

--- In oberheim@yahoogroups.com , "Paul J. White" <pjwhite@...> wrote:
>
> I can't really help with Oberheim's history beyond when I left
> Oberheim in July 1986, but I remember they were starting to produce
> black-face Matrix-1000s around that time. So there would have been
> about 6 months of production going on before 1987.
>
> -- Paul White

> At 09:11 PM 4/22/09, you wrote:
> >Hi, I would like to know if this is correct...
> >When Oberheim was still in business, they made the Matrix-1000 with
> >the black face.
> >Then Gibson Guitar bought Oberheim in 1986 and from then on all
> >Matrix-1000 had the white face.
> >It was Gibson's idea to make the face white and any white
> >Matrix-1000 were manufactured by Gibson Guitar.
> >Is this correct
> >
> >I have checked wikipedia and vintagesynth.com and there seems to be some
> >date errors like, if Oberheim closed in 1986 when gibson bought them
> >(wiki) and vintagesynth.com
> >sates matrix-1000 production was from 1987 to
> >1994 then there would be never any black face units.
> >
> >If any one could help to know when the white face started I'd really
> >appreciate it.