accuracy of dating 1680's using serial number

[eickofjp]

I have a Submariner 1680 with a serial date 278xxxx. It is not a "Red" Submariner. My limited research of dating via serial number indicates manufacture 1970-71 by most sites. however research also indicates the "Red"
was manufactured 1969-1973. After 1973, all lettering was changed to white.
Were there both red and white lettering 1680's manufactured between 1969-1973? if no all white lettering in that time period, why would my watch date to that that period(1969-73) based on serial number?
Appreciate the help.

[Tools]

There were Subs with red lettering, also white with red overstamps that faded to pink, and many reds were replaced with white dials for no good reason.