...the 15xx sample shown was not for 1570 (1570 is not equipped with a date complication) but for 1525 and fits further 15xx references as mentioned.
The question regarding the appearance of round 3 and open 6/9 - including 26, important detail - has been answered, it's your #1, so I think around 1980 (perhaps a bit later because there's another version I assume as a short-life transitional around late 70s/early 80s, with all 6/9 open but still flat 3).
About the ring, can't tell for sure. I've only seen one piece round 3 all 6/9 open with this, so I assume most come without - but I wouldn't take it as a service part indication (as you probably think about).
Just to mention, these are observations and assumptions only, it's a difficult topic - either a date wheel is mounted and therefore not visible in detail, or it's not mounted and you can't be sure about it's origin.
This message has been edited by Xeramic from IP address 18.104.22.168 on Apr 6, 2018 3:57 PM