A missing episode date should stay unknown. Replacing it with today's date makes old content look new and can change the meaning of a “recent episodes” screen.
There are several dates in a podcast system. A publisher may provide a publication date. Your catalog may record when it discovered or updated a record. Your app may record when the listener saved it. Those timestamps are useful, but they are not the same event.
Pick labels before formatting
Use “Published” only for the publication field your provider documents. If the value is absent or invalid, show a quiet fallback such as “Date unavailable,” or leave the label out when that keeps the card clear.
Do not parse dates by cutting a timestamp at a fixed character position. Use a parser that understands the documented format, then format the result for the listener's locale. Keep the full value in your model when it is available.
For date-based sorting, define what happens to missing values. They might appear after dated items, or in a separate section. The important point is to use one consistent rule rather than an accidental conversion to the current time.
Test the boundaries
Include a value just before midnight UTC, one with an explicit time-zone offset, an old date, and no date at all. Check the result in two time zones. A date-only label can legitimately differ across zones when it represents a precise instant.
If your product needs a calendar release day rather than an instant, preserve that distinction in its data model. Good labels prevent a technical fallback from becoming misleading information for a listener.