Fed Tax Withheld on 1040 is much greater than total of withholding on W-2s

Debugging an issue the IRS identified for me from 2018. I need to figure out whether TT made an error totaling federal tax withheld. TT itself seems to disagree internally, but there is probably some logic to this.

These are the relevant numbers:

  1. W-2 withholding (Box 2) totals $19,091.79 – I totaled this by hand, and TT's own W-2 summary screen shows this amount.
  2. TT-generated 1040 (p1 line 16) says $23,704

I'm at a loss as to why these two numbers aren't equal.

Does anyone out there have insight into how TT calculates total federal tax withheld for the 1040? 

Does TT include any other payments or withholding when calculating the second number? Or could I have checked a box wrong somewhere?