On Ebook Central, when a title is held with more than one access model, we have defined the order in which each access model is used. The hierarchy is as follows:

1.Unlimited Access (UA)
2. Subscription
3. 3-User (3U)
4. 1-User (1U)
5. Non-Linear Lending (NL)
(See Ebook Central: Access Models for details about access models)

When a title is held with multiple access models and is accessed by a user on the patron platform, the platform will display availability information for the copy that is available for use by that user. Because there is no concurrent user limit on UA or Subscription titles (in other words, they are never ‘in use’ and unavailable for other users), this is most apparent when a limited-user license (1U or 3U) is owned in conjunction with an NL license. For instance, when a book is owned in 1U and NL, the 1U is used first, and the availability message seen by the first user to access says that the library has access to 1 copy.

availability message showing user will access 1U copy

Once the first user is actively using the book (meaning the 1U copy is no longer available for other users), access flips over to the NL copy, and the NL availability message displays instead (access to "multiple copies").

availability message showing user will access NL copy - text shows multiple copies available

Because of this, you may see availability messages for popular titles flip back and forth.
Please note that any access permissions settings on limited-access models set in LibCentral will apply when the limited-user copy is accessed. For example, if you have disabled downloading on 1U titles but not NL, availability of the full document download feature will appear to toggle back and forth based on whether the 1U copy is in use. If you would like to prevent this, you can use the ‘download days’ setting instead of the checkbox to disable downloading for 1U titles (set download days to 0), and then use book specific permissions to override this for specific titles that you also own in NL (see the Access Permissions help guide in LibCentral for more details about these settings).
Admins can check to see if a book is held with multiple access models in LibCentral. All access models will show on the book’s details page.

Detail page on LibCentral showing 1U and NL copies owned

We realize that the changing availability message may be confusing for users. However, with the current access hierarchy, we can prevent premature expiration of the annual loan-days for high-use NL titles when a 1U or 3U copy is also available.