all three of those are post mid 1977 production
look at this picture and the relation of the "S" to the "P" in "Speedmaster"
http://speedmaster101.com/wp-content/uploads/2016/04/P4290005.jpg
The 2 on the left are 74-mid 77 production and the "S" does not drop to the bottom of the "p" The 2 on the right from mid 77 to mid 80's dials and the S drops to the bottom of the p. Note this test would only excluded early -76 models that have not been serviced, any watch that was serviced from 77 to mid 80's would have the second dial, so a serial number is still preferred..
What are your thoughts? From those pictures its hard to make an evaluation or exactly date the watches. Different lighting, and in at least 1 case heavily filtered in instagram
you can read more here.
http://speedmaster101.com/145-022/145-022-71-74-76-78/Click to expand...