>The number of the “Express Mail” mailing label was placed on
>the paper(s) or fee(s) that constitute the correspondence prior
>to the original mailing by “Express Mail;”
当方（US）PTO なんかにもときどき電話しています。
"The number of the “Express Mail” mailing label"
is the tracking number for the original mailing by Express Mail.
The applicant places this number in the
"Express Mail Label No." box
in the form entitled
"Utility Patent Application Transmittal".
You can easily find this form (PDF) at the USPTO site.
という風に従来の出願方法は熟知しておりますが、
original mailing by Express Mail Tracking Numberは
original mailing by Express Mail
の前には解らないはずなので、この文章は変ですね。
