I have records with a Deliverable of Blank but a DPVCode=Y. If they have a DPVCode of Y why wouldn't the Deliverable be Y also?
This doesn't happen much but usually it is because the address is marked as "Vacant" (there is a Vacant field in which a "Y" is present if the address is vacant).
The USPS determines that an address is vacant after they make their daily deliveries and the mail box keeps filling up. After a predetermined amount of time (probably 3 to 4 weeks, but that is a guess) that the mail has not been removed from the mailbox, the postal carrier will determine the address to be vacant. The mail is then stored at the post office for a time. The resident would have to notify the post office to tell them the address is not vacant.
So, DPVCode=Y means that the address is a valid deliverable address but we perform an additional calculation that includes the Vacant field. If an address is vacant most people would want to know about it so they don't ship to that location. That's why we do it this way.