Open 6s and 9s on 16800 date wheels

[Chronos22]

I would appreciate the assistance of experts. I have been offered a 1983 16800 Submariner. It has closed 6s and 9s on the date wheel. This made me doubt the originality of at least the date wheel. I checked my saved sources and realized that none of them clearly state when Rolex ceased using these date wheels on Submariners.

I need confirmation or correcting of the following statements please:

(1) Open 6s and 9s (O69) started with 1680 Subs but continued in 16800 Subs.
(2) O69 in 16800 Subs ended when glossy dials were introduced (I believe this happened in 1983)
(3) O69 were used in all 16800 Subs
(4) O69 were also used in 168000 Subs
(5) When Subs that were issued with O69 date wheels were serviced by Rolex and the date wheel needed to be replaced date wheels with closed 6s and 9s were installed when Rolex ran out of O69s.

I appreciate your responses!