Mike gave me a number of documents with Coco.
MOT documents, tax discs, a few V5's.
First registered in July 1960
Not sure what colour..
OYM 609A
Was given to the vehicle after the previous registration number SJD 977 was sold on, probably for the profit, as old three numbers, three letters, are more desirable than a suffixed number plate. It was still on the vehicle on 27th Oct 1989.
And the first time I have found OYM 609A is on paperwork from 18th July 1990 on a V5c document when the ownership changed from Ms Sarah L.L. to Mr Hugh E.B. Also found between MOT certificates from 1989 to 1991 the mileage makes sense too, gaining only 7000 miles in the two years, so it all looks pretty good.
So somewhere in that nine months the registration number was changed over. I wonder where the old plate went ?
I've also read that the OY in the OYM 609A, refers to the county or city from where the vehicle is registered. OY = Croyden. So i'll look into this some more and see where the vehicle was registered at that time. I also think that it was given a suffix plate as early or as close to the original first registration date as possible. So the ABC 123A type plates were only released a couple of years after the car was first registered, from Feb -31 Dec 1963.
So i'm the 5th owner, and I have some correspondence between a couple of the previous owners in the form of letters and notes on payments or changes to the standard vehicle.
This page on Wikipedia helped today Understanding UK registration numbers