But the IRS can, and sometimes will, change your withholding number. And at the request of others, despite what you enter on the form. Unless you can prove to the IRS that it’s accurate (you really do have that many kids).
I know this from working for some years in Child Support Collections & Enforcement.
I worked on one of the first projects where we filed claims with the IRS to seize the income tax refunds of deadbeat parents to apply to their unpaid child support. We collected a whole lot of money for those kids, and made a whole lot of deadbeat parents really angry. Tough!
Many of them thought they would be smart and prevent that seizure the next year by having no refund, so they jacked up the number of exemptions on their W-4, claiming numbers like 25, 50, or even 99 dependents.
We promptly filed a document with the IRS, stating that this was an incorrect number of deductions; that the correct number of dependents for person ______ was __ (which we figured from our records of his/her children from various spouses, and who were still under legal age).
Based on this, the IRS sent them (and their employer) a letter saying that due to conflicting information, they were resetting the W-4 deduction number to that used the previous year, and explaining the evidence they could send to the IRS to prove that their claimed number of exemptions was correct. Which they mostly couldn’t do, since it was a made-up number.
Of course, this was criminal deadbeats trying to evade supporting their children.
For normal people, the IRS doesn’t care if your number of claimed deductions is too high, too low, or just right – it all works out when tax filing time comes.