Everytime you create a new numbering pattern in serials you can save it for later use. These patters are accessible via the Manage numbering patterns page.
Get there: More > Serials > Manage numbering patterns
This page will list for you the numbering patterns you have saved in the past as well as a few canned patterns.
If you have upgraded from a previous version of Koha you will see 'Backup patterns' listed for patterns used in version before Koha 3.14. This is how Koha saved your old numbering patterns. You can edit these to give them more meaningful names from here.
It will also allow you to create a new numbering pattern without first adding a subscription. To add new new pattern click 'New numbering pattern' at the top of the list of patterns.