Rob-you are correct that ground chuck is from the shoulder,round from the back leg,sirloin from the sirloin,etc....that is the way it should be,but i have only seen inspectors so far testing the percentage of fat in the different labeled grinds,i don't think they have the testing equipment so far to determine where from off the animal the beef is from,only the fat content....and yes,most places use the trimmings from the days cutting when they grind it and selling it as (ground beef)....the grinds labeled ground chuck or round,sirloin,etc,usually come in from the packers,where they have federal inspectors on duty when ever any processing is done.If you have your own grinder by all means grind your own-no questions then on what you have.