On the "Checkout history" for a record (/cgi-bin/koha/catalogue/issuehistory.pl?biblionumber=85452), there is a column called "Patron", which holds the borrowernumbers of the patrons that have borrowed items connected to the record. If old loans are anonymized, this will show the same borrowernumber as AnonymousPatron. 

If you do not remember the setting for AnonymousPatron you might not understand that the loans have been anonymized right away. It could be more helpful to display something like "Anonymized" instead of the AnonymousPatron borrowernumber.