I think that one ../ is missing below:
// module app/billing/billTo/Customer
define(function (require) {
[...]
// BAD: normalizes to "../util/date" -- a URL, not an ID!
var Date = require("../../../util/Date");
Should probably read:
// BAD: normalizes to "../util/date" -- a URL, not an ID!
var Date = require("../../../../util/Date");
Also congrats on a really awesome tutorial!