It’s possible that Form 540, Line 16 might also be reflecting an amount from Schedule CA (540) Part I, Line 27, column B.
According to Line 27 – Total in the Part I Instructions of the 2021 Instructions for Schedule CA (540) in 2021 California Form 540 Instruction Booklet:
Subtract line 26 from line 10 in column B and column C.
Also, transfer the amount from:
Line 27, column B to Form 540, line 14. If column B is a negative number, transfer the amount as a positive number to Form 540, line 16.
Line 27, column C to Form 540, line 16. If column C is a negative number, transfer the amount as a positive number to Form 540, line 14.
[Bolding mine.]
So, if Line 27, column B is negative, it would also figure into the Form 540, Line 16 calculation.
