As a test to see whether my apt server might be out of date, I tried deleting the "us." from all the URLs in my sources.list. After an apt-get update, an apt-get upgrade resulted in "0 upgraded, 0 newly installed, 0 to remove and 9 not upgraded." So it looks to me like there was no problem with my apt server being stale.
As a test to see whether my apt server might be out of date, I tried deleting the "us." from all the URLs in my sources.list. After an apt-get update, an apt-get upgrade resulted in "0 upgraded, 0 newly installed, 0 to remove and 9 not upgraded." So it looks to me like there was no problem with my apt server being stale.