Succinct phrase that covers both “not started” and “previously started, later stopped”

Pending might fit also as a technical term.

Also, there are words that can be used in its definition:

remaining undecided; awaiting decision or settlement; unfinished: pending business; pending questions; pending litigation.

An example usage from an IBM product description:

Pending tasks are tasks that were not run and are not scheduled to run.

Also, outstanding might fit.

An example usage from SAP Status Management:

This means that, for example, a notification can be put in process, even if it contains outstanding tasks that have not yet been released.

"Shelved," "On Hold," or "Inactive" would suffice. I like "Shelved," personally.