Read the format's default
The official XMLTV DTD documentation says that an omitted timezone is interpreted as UTC. An importer should not silently replace that meaning with the server's timezone or the viewing device's current location.
For an invented timestamp containing a complete date and time but no offset, record both the raw string and its UTC interpretation. The production server running in a different zone does not change the source format's meaning. A local display conversion belongs to a later, explicit step.
Keep a questionable feed questionable
A supplier may have intended local time while omitting the offset. Do not repair that assumption invisibly in the general parser. Record a documented source-specific exception or seek corrected source data, retaining the original value and reason for any transformation.
Compare a small known interval before applying a bulk correction. A title mismatch may reflect scheduling changes, a channel mapping issue or a different feed, rather than a timezone alone. An apparent whole-hour difference is a clue, not proof.
Separate parsing and presentation
Store the accepted instant independently of the display zone. That allows one guide to be presented for different readers without rewriting the underlying schedule. Keep the display zone and date in any screenshot used to review a reported mismatch.
Do not use the current offset to convert every date in a multi-day feed. Apply the chosen zone's date-aware rules through the application's maintained time library. This article states the format default and an importer workflow, without claiming a specific region's current clock-change law.
Questions answered
Does no timezone mean the importer can use its own local zone?
No. XMLTV's documented default is UTC.
What if the feed clearly intended a different timezone?
Treat that as a documented source-data exception or correction, preserving provenance rather than changing the global default.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.