3GPP 24.501 v20.0.0 — the document's own text
5.2.2.3.8 INITIAL-REGISTRATION-NEEDED
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
The UE shall initiate the initial registration procedure, if still needed, as soon as the access is allowed in the selected cell for the UE.
The UE may initiate registration procedure for emergency services.