Several podcast series use this designation for their introductory or foundational episodes:
The most prominent "S1E0" titled "Origins" (or often "Prologue") is the double-length pilot for the anime series . [S1E0] origins
Features an episode titled "S1E0 – Origins" that sets the stage for the show's exploration of cult and low-budget films. Several podcast series use this designation for their
Occasionally, this alphanumeric string appears in massive technical text dumps, such as SEC EDGAR archives, but usually as part of a longer random identifier or specific internal code. Ownership S1E0: 8bitpenis (Ownership) | Solana Media such as SEC EDGAR archives