Ignorance is certainty that you don't know something. That means you cannot bring up any information about it when you try to. However, that only applies to the moment.
Knowledge is justified belief. ( sufficient to accept a particular fact or take a particular action ) It's perfectly possible that you have knowledge about a subject that you simply don't recall right now, but which will return in a different context. This is a typical human experience.
Therefore, ignorance is not an epistemic 0, it's actually 0.1. It has a pragmatic place in a logically necessary taxonomy of evidentiary value:
0 unknown unknowns
0.1 ignorance (certainty that you don't know)
1 found anecdote (assumed motive)
2 adversarial anecdote (presumes inaccurate communication motive)
3 collaborative anecdote (presumes accurate communication motive)
4 experience of (possible illusion or delusion)
5 ground truth (consensus Reality)
6 occupational reality (verified pragmatism)
7 professional consensus (context specific expertise, best practice)
8 science (rigorous replication)
<- empirical probability / logical necessity ->
9 math, logic, Spiritual Geometry (semantic, absolute)
10 experience qua experience (you are definitely sensing this)