If a memory feels completely gone, does that mean it was erased?

Not necessarily — forgetting is frequently retrieval failure, where the trace persists but is momentarily inaccessible.

The everyday experience of a name on the "tip of your tongue," or of instantly relearning something you thought you'd lost, shows that "forgotten" and "erased" aren't the same. In the storage/retrieval framework, such items still have real storage strength; what dropped was retrieval strength. This matters for studying: because the trace is often still there, the right retrieval practice can restore access far faster than learning from scratch — and each restoration deepens storage.