Thanks Bill, USPS tracking does work using the Customs Form number!
Being a mail order operator (Gold Medal Models), I have amassed over 25 years of experience in dealing with the postal systems of several countries.
Today, there are two customs forms available for small shipments like we are used to. The small one provides tracking only within U.S. borders and is used on envelopes and very small parcels. It will not be trackable in Canada or other countries. Also, there is little to no insurance coverage available with this form.
The larger form is for larger parcels or oversize envelopes and will provide tracking services to virtually all countries. Insurance options are also greatly improved and coverage varies from country to country according to a USPS chart available at the post office or online. For example, when I ship overseas, insurance coverage available to Japan ranges as high as $5,000 per parcel whereas coverage to the U.K. is only $650.00. These services cost extra when postage is purchased.
I use these services with Priority International Mail mostly, but in some cases I have to use Express International to get the insurance coverage I need as in the case of the U.K. and the rates are higher because of this.
Gold Medal Models orders to individual customers are usually shipped in No. 11 business-size envelopes with thicker than usual paper and internal cardboard stiffeners. I used to be able to send them as regular envelopes stamped Hand Cancel on the outside and at ordinary letter rates. But now the USPS has changed all that.
If the envelope is stiffened as are mine, they now are classified as "non-machinable" and the rate is much, much higher. What used to cost me $3.60 to ship to Canada now costs me $9.65. And the USPS isn't cutting me a bit of slack even though the local post office people love me for all the business I've brought them over the years. We're practically family, but their hands are tied on this one.