Fubaar,
Better not fly on any US carriers overseas then. Happens everyday. Guy comes off a MD80 or 737 (either as a captain or first officer, depends on seniority) never seen the front end of a wide body, never been overseas (unless you count going over one of the great lakes to Canada) and gets plopped down in the left seat. You bet they will put an experienced f/o with him. Has he been trained? You bet, but probably doesn't know squat about what he his doing.
This is of couse is the extreme, but does happen--often. Works the other way too. Guy has sat in the right seat for DECADES flying ULR. Next thing you know he is doing five sectors a day, in and out of TRWs in a narrow body in the left seat. Has he been trained? You bet, but probably doesn't have a clue on how to manage his new enviournment.