Hi Steve, I would like to add some pieces of info. here in accordance with some Japanese documents I have.
1) There were only 2 GS models having the word "Chronometer" on them; namely a) the GS3180 released in 1960 (widely known as the GS first model) by Suwa Seiko, and b) the GS second model released in 1963 (GS430 for the first batch and GS5722A for the second batch -> both=18,000 vph) also by Suwa Seiko.
GS3180 (the GS first model) with "Chronometer" on its dial only
GS430 (the GS second model made in the first batch) with "Chronometer" on both its dial and its movement
GS5722A (the GS second model made in the second batch) with "Chronometer" on both its dial and its movement
It is noted that the GS second model made in the third & fourth (last) batches GS5722B no longer came with "Chronometer" but "GS" mark instead. The production start of GS5722B was estimated to be from 1966. Since Seiko was unable to use "Chronometer" any more, the Seiko's own stricter accuracy standard (than that of "Chronometer") was introduced, making Seiko increase the VPH of 5722B to 19,800 vph.
Your GS second model 5722B was the third batch in my opinion. It is typically understood that a difference between the 5722B third batch and the 5722B fourth batch is the size of a "GS" mark on the dial. The 5722B third batch came with a slimmer but taller "GS" mark in comparison with that of the 5722B fourth batch.
Your GS5722B (the GS second model made in the third batch)
GS5722B (the GS second model made in the fourth batch)
2) Concerning the GS Astronomical Observatory Chronometer, it was made by Kameido Seiko (Daini Seiko) based on the no-date GS45 model (36,000 vph). The GS45 is considered the last vintage hand-wound GS after GS3180, GS430 or 5722 and GS44 (known as the most mysterious GS).
Seiko marketed this GS45 Astronomical Observatory Chronometer (like GP Gyromatic Observatory Chronometer as you've mentioned) maybe in 1969. According to my documents, it was 73 out of 103, passing the Astronomical Observatory Chronometer. It was designated as 45GSN cased in 18KYG. The price in 1969 was 180,000 JPY, which was almost 2 times that of the GS45VFA (SS-cased) of 100,000 JPY.
45GSN Astronomical Observatory Chronometer (18KYG) -> Dial & Movement
The Concour Certificates and the movements displayed at The Seiko Institute of Horology (Kameido, Tokyo)
Hope my info. given above helps add more contents to this very interesting topic.
Regards, Joe