Some areas have duplicate, or very similar street names (ie, 'ave' vs. 'street') I don't think its that much of an ask that a website lets you enter your address correctly
FWIW I have received mail from the USPS in places that had no canonical full address as well. It's not the case in reality that the USPS only delivers mail to mailboxes that have an associated entry in their canonical database here in "messy" reality.
