Part of the problem , beside maybe more than one assembly line is when parts ceased production. When the did the head switch at 26,xxx they may have stopped making that variation, a month or more before parts got used up.
The gold tanks available at part # 19,xxx, but they had to be made before that.
But I am reasonably sure if you ordered a gold one, it would be stamped 19,xxx or higher number . And delivery before start of year 1970 may not have happened..