The more I think about it, the more I find it implausible that Den's parents went to Europe purely to escape the awkward social circumstance of being around town in the aftermath of Bobby Black's death. That's a lot of travel in those days, and depending on exactly when the story is set the Atlantic might be full of German U boats. They could have gotten out of town much more conveniently by renting a townhouse in Chicago for a bit. Plus, would they not have taken Den along? He's the one most directly responsible, after all.
I'd suggest Alden conflated those events in his mind as a child. If so, what is Wolfe trying to clue us into? Were the Weers somehow involved in international business? Were they trying to settle something related to broader world events, like the stagnant economy in Western Europe? Can we relate it to the story of St. Brandon's ship that has one side in America while the other side still hasn't left the dock in the old world?