State mandatory taxes is using numbers from one of the W2's box14 but not the other

I am on turbotax desktop mac version. I noticed that my state and local taxes worksheet show a "mandatory state tax" line which uses the numbers from box14 (sum of SDI and RSU) of only my spouse's W2. It is not taking the numbers from my W2 box 14 (VPDI). Of course this is only an assumption on my part as turbotax forms dont show exactly how they calculate the line 17 in that worksheet for "mandatory state tax".

I have searched for info on this but not very clear. Can anyone clarify the following for me:

1. Does both RSU and SDI need to be added up for state mandatory tax?
2. Are there any exception cases where RSU from one individual would not need to be added up but other would need to?

3. Are there any ways to find out how the line 17 is calculated?

Thanks,

posted