1. Esri ArcGIS Pro Documentation. "System tables of a geodatabase in Oracle." This document explicitly states, "The TABLEREGISTRY table... contains a record for each business table that is registered with the geodatabase... The registrationid column contains the unique ID for the table registration, and it is used to identify the business table in other system tables." It also clarifies that for the LAYERS table, the layerid "corresponds to the registrationid in the TABLEREGISTRY table," establishing the latter as the primary source.
2. Pennsylvania State University, GEOG 868. "Lesson 4: Versioning." The courseware explains the versioning architecture: "When a feature class... is registered as versioned, two tables, called delta tables, are created. These are the adds (or A) table and the deletes (or D) table... The A and D tables are named using the RegistrationID of the feature class as it is stored in the SDETABLEREGISTRY system table." This directly supports using the table registry to find the delta tables.