The ileum is some 20 foot long, the last 3 feet are the terminal ileum. A colonoscopy can only view about
18 inches of that terminal ileum, if that. Many colonoscopies they never penetrate the ileocecal valve and get a good look at the terminal ileum.
Crohn's disease TENDS to move UP the digestive tract, not down. The colonoscopy only gets to inspect that last part of the digestive tract.
And sometimes altho there is no sign of Crohn's visible to the scope, the biopsies tell a different story.
The barium series has a good chance, altho not perfect, of detecting problems in more of the ileum (small intestine) and way beyond what the colonoscopy can reach or inspect.
IF the barium series reveals no answers and your husband's symptoms persist then I would be insisting on the Pill Camera Endoscopy. And if he has a history of resection or strictures I would further insist on the Agile Patency Capsule first to be sure that he can pass the PCE w/o a problem.
Crohn's can occur anywhere from the mouth to the anus so the colonoscopy leaves a lot of territory unexamined. Its been the "gold standard" for Dx'ing Crohn's for years ONLY BECAUSE the majority of Crohn's disease activity begins in or at the terminal ileum/ileocecal valve (the end of the ileum and beginning of the colon).
My Crohn's began in the MID-ileum and still has NOT struck the terminal ileum w/in reach of the scope. (knock, Knock, KNOCK) and I was first Dx'd in 1975 and had my (only) resection in 1978 (knock, Knock, KNOCK).