It appears you are looking in the First Day section of the UPSS website.
What you want is the section for the "Earliest Reported Date of Usage" section, which is what was given in my earlier link:https://www.upss.org/erp/index.php
If you go there, and select by Scott No, using "U408", they report
the ERP as: Aug. 22, 1907.
There are two other varieties of U408, and dates are given for them as well.