At the end of the sixties the two top series of watches from Seiko were Grand Seiko and King Seiko. The introduction of Quartz watches at the end of 1969 not only meant that the mechanical watches from Switzerland was endangered but also the Japanese.
Everyone wanted the latest and greatest, quartz! With a precision that was way better than any mechanical watch and the coolness with something modern, electronic on the wrist Seiko also discontinued the Grand Seiko (the GS label did not reappear until 1988 as quartz and 10 years later, 1998, as mechanicals with the 9S caliber) and the King Seiko lines around 1973-1974.
Quartz was a new thing and their was a steep evolution during this period, from the earliest with a precision of +/- 15 seconds per month to +/-10seconds per year.
In addition to this you also had the Superior line which in 1978-79 reached +/- 5 seconds a year. Approximately 25 different movements were developed during a period of less than 10 years.
The table is by no means complete, e.g. the 0853 and 5856-movements are not in.
Personally I think these watches are very nice to collect. They are, still, cheap, are available in many, many different variants with different movements, dials and cases. I think that Seiko took the inspiration for many of their modern GS dials from these.
I like the 484x and 48Sx models best as they are wider up to 38mm in diameter and thicker than the later ones. Getting one of these is a cheap way of having a watch with some GS 61/45 feeling.
Despite the fact that these are ~40 years old I have only had issues with the 5856 equipped ones. What you should do is to check and replace the seals to the small battery hatch as they are often completely dry. The symbol at 6 o’clock on the dials is a (or in the case of the twin quartz movements, two) stylized quartz crystal and nothing else…
9923-701A & 9923-501A