Two 01:30 timestamps are not necessarily duplicates

The NIST 2026 schedule places the US fall-back transition on November 1 in participating regions: NIST daylight saving time rules. This does not describe every country or every US region.

Consider two completely synthetic CSV rows:

If an export keeps only the clock text, both look like 01:30. With their explicit offsets they describe instants an hour apart. That can matter when reviewing logs, market-data exports or other time-series records. It does not prove that any particular pair of records is unique: use the rest of the source contract.

The standard library can demonstrate the distinction:

from datetime import datetime, timezone

a = datetime.fromisoformat("2026-11-01T01:30:00-04:00")
b = datetime.fromisoformat("2026-11-01T01:30:00-05:00")
assert a.replace(tzinfo=None) == b.replace(tzinfo=None)
assert (b - a).total_seconds() == 3600
print(a.astimezone(timezone.utc).isoformat())
print(b.astimezone(timezone.utc).isoformat())

Keep the original timestamp, inspect complete values and establish whether sorting compares text or instants. If the offset was never stored, simply adding a timezone afterward does not establish the original instant. Named zones, ambiguous local times and parsing policies need separate checks.

RowCove can help inspect the original fields in supported local files; this is not a claim that every reader automatically reconstructs missing timezones or normalizes all timestamp representations. The calculation above is independent Python. Check the output before passing a transformed file to the next step.

Disclosure: RowCove team, commercial local data tool. AI-assisted draft, generated mock rows only. No customer, trading strategy, real event feed or performance measurement is included. Video assets illustrate these rows; they are not a recording of the RowCove interface.