I'm not sure I agree with this sentiment. If a USC petitions for someone outside the country to be able to enter and gain immigrant benefits, I can see that DOS wants to know if the USC is not doing anything fraudulent and may need to check out their background some. The government issued the SSN and another branch is asking for it. The only issue I see is the impracticality for some who have been divorced for a long time to track this down. The issue is whether the ex should allow you to give out her SS #. I say no, speaking from her point of view. If she's willing, of course there's no problem. I'm just suggesting she shouldn't be, and GUZ shouldn't be implying that it's needed.