Multiple Ulcers?

Recently, my father was diagnosed with multiple ulcers of the stomach and duodenum (7). The doctors are pretty sure it's not Zollinger-Ellison Syndrome (1 in a million chance). Why could he have so many? Is this really abnormal and, most of all, serious?

There's a lot on the net about ulcers but not as much about cases of multiple ulcers (unless you have Zollinger-Ellison Syndrome). Has anyone had this problem before?