There are 3 distinct overdue blocks that can be applied in ALEPH. These blocks work independently from one another. You can choose any combination of these to apply for your institution, but they will apply (or not) for ALL of your institution.
Block if single item overdue AND X notices have been sent
1. There is a setting that defines an item as "overdue" when it is past due, and 1 or more overdue notices have been sent.
Most institutions have this setting at 1, meaning this block will apply when an item is past due and 1 or more overdue notices have been sent. The ALEPH system checks whether or not notices have been sent whenever a patron tries to loan or renew materials either through the staff client or the Web OPAC. Although this check doesn't create a block in the patron record, it does prevent renewal of any items, overdue or not, if one item is blocked according to these criteria.
Block if X number of "overall" items are overdue
2. Another setting defines how many overdue items a patron can have before being blocked. This will block loans and renewals for patrons with that number of overdues, regardless of whether or not an overdue notice has been sent. One value can be set for "regular" overdues, and another for "recall" overdues. If you want to use it, I can increase the number of overdues a patron can have before they are blocked and reinstate the system check that looks for this.
Global Block when an item is X days overdue, block applied at return
3. The third type of block is a default system setting that defines how many days overdue an item can be before a patron is blocked. This setting actually creates a block in the patron record (the "70" block) which could prevent other patron privileges, not just loan and renewal, if desired.
Since this block does not occur until after the item is returned, this block is not heavily used.
*In addition, there are other blocks that were added in Version 18, which block patron privileges for a time equal to, or by a factor of, the amount the item was overdue.
The block is not placed until the item is returned.
These blocks are setup in Circ policy, and can be by patron/item status combination (not global). More information at New Functionality Document, under V18 Functionality Combined.
This is the least popular blocking method.