Upper ext u/s noted unable to compress the innominate vein. several head/neck/chest sx, incl. pain/swelling. could something be missed on u/s?

Yes: This needs to be checked out since an US can miss something compressing a blood vessel;especially since you have symptoms.

It's possible: The innominate vein usually cannot be compressed by ultrasound because of its location in the chest behind the ribs, sternum, and/or clavicle. I'm not sure why that would be stated in your ultrasound report. If you are having persistent pain and swelling, it should be examined for possible causes.