And how many get cancelled each year because they are not
being paid for, and if they do it's much easier to remove a
domain name from the internet. Unless there would be an
active system with signatures it's very hard to make sure
cancelled PI/PA blocks will disappear from the DFZ.
First of all, if a PI block is not paid for it will disappear
from RIPE's DB. I would expect many ISPs to have an internal
process for IPv6 Peering customers to regularly check the DB.
Also, there are a number of groups which regularly analyze BGP
announcements looking for things like bogons and ghost-routes.
I would expect one or more of those groups to include unregistered
PI blocks in their reporting. A greater number of ISPs will
probably track these reports to make sure that they are
following best practices.