#9375 was a 1985 model so I would suspect that your car was built in '83 or '84 by the serial number and would most likely be a GT5.
As far as your original question, nobody knows what the exact production numbers are of either GT5-S or GT5 cars - Peter has gone a long way to giving a good idea, but until the registry is complete nobody will know for certain.
You can rest assured that it is a quite rare care. They were building roughly 20-30 cars a year when your car was built.
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