Two people using the same lunar birth month can have Zuo Fu and You Bi at matching branch positions but different San Tai and Ba Zuo placements. The latter pair also depends on the lunar day.
Count the starting cell as day one
In the common rule, San Tai starts at Zuo Fu and moves forward through the branch sequence. Ba Zuo starts at You Bi and moves backward.
For an illustrative first-month calculation, Zuo Fu is at Chen and You Bi at Xu. On day one, San Tai and Ba Zuo remain at those starting cells. On day two, they move to Si and You respectively.
These are branch positions, not necessarily matching palace names. Different birth hours can change which life area each cell represents. Leap-month treatment must also be consistent.
Because the placement rules are connected, four labels do not amount to four independent pieces of evidence for a promotion. Traditional interpretation still needs the Career Palace, main stars and relevant timing layer. The arithmetic does not determine a person's job title.