wantmygcnow,
Thanks for the explanation and I think I don't have to go to InfoPass now. His GC would come in a month or so.
I think you should still take an INFOPASS. It is not completely clear what exactly happened and you won't know for sure until you talk to USCIS.
As I remember, when someone enters the U.S. on an immigrant visa, that person has to complete some form, including the current address. The green card is then mailed to that address.
See http://germany.usembassy.gov/visa/entering_iv.html
"The Department of Homeland Security will mail the card to you at the address of final destination you give at the time of your admission to the U.S. as an immigrant."
You don't know if you son completed such form and if he did not, the paperwork needed for his new card may not be complete.
You need to be proactive here, IMO.