Series are known as Serial Associations in Logos 3 and you could create your own in addition to the ones created by Logos. Thanks to v5.1 you can now create your own Series, or modify the Series name given by Logos.
Simply select one or more resources in Library and then click the Information button when you will see the existing Series name or an invitation to "Set series...".
If you don't like the 2-volume series name EBC Abridged Edition then change it (make sure you select all volumes in the Series).
Want to link a single-volume NT commentary to a single-volume OT commentary? Select the two resources, click where it says Set series for all and type the name you want. Then you can prioritize the new series.
The feature is very flexible in that you can use any of the their data types to switch between resources e.g. use TDNT # to switch from TWOT to TDNT and then use TWOT # to switch from TDNT back to TWOT. Alternatively, if you set "Send hyperlinks here" the same tab will be used for external hyperlinks to TDNT and TWOT numbers.