刚刚查到的资料，为什么仍可能已经过时？

"""Offline application policy, NOT an HTTP cache or a truth verifier."""


def decide(record, now, target_time, recheck_after):
    # All times are integers in the same fictional time scale.
    # target_time = when the question's fact should apply; now = evaluation time.
    if record["status"] != "ok":
        return "unavailable"
    fetched = record["fetched_at"]
    checked = record["checked_at"]
    if fetched > now or (checked is not None and checked > now):
        return "clock_error"
    start, end = record["valid_from"], record["valid_until"]
    if start is None or end is None:
        return "unknown_period"
    if start >= end:
        return "invalid_period"
    if not start <= target_time < end:  # Our explicit half-open policy.
        return "outside_period"
    if checked is None:
        return "needs_recheck"
    if now - checked >= recheck_after:  # Boundary itself requires rechecking.
        return "needs_recheck"
    return "candidate"  # Still needs source, scope and claim-support checks.


base = {"status": "ok", "fetched_at": 100, "checked_at": 99,
        "valid_from": 90, "valid_until": 110, "revision": "r1"}
cases = [
    ("fresh_fetch_old_period", {**base, "valid_until": 95}, 100, "outside_period"),
    ("fresh_fetch_old_check", {**base, "checked_at": 80}, 100, "needs_recheck"),
    ("current_candidate", base, 100, "candidate"),
    ("historical_question", {**base, "valid_from": 0, "valid_until": 90}, 70, "candidate"),
    ("missing_period", {**base, "valid_until": None}, 100, "unknown_period"),
    ("failed_tool", {**base, "status": "error"}, 100, "unavailable"),
]
for label, record, target, expected in cases:
    actual = decide(record, now=100, target_time=target, recheck_after=5)
    assert actual == expected, label
    print(f"{label}: {actual}")

assert decide(base, 100, 110, 5) == "outside_period"
assert decide({**base, "checked_at": 95}, 100, 100, 5) == "needs_recheck"
assert decide({**base, "checked_at": None}, 100, 100, 5) == "needs_recheck"
assert decide({**base, "checked_at": 101}, 100, 100, 5) == "clock_error"
assert decide({**base, "valid_from": 110}, 100, 100, 5) == "invalid_period"
assert decide(base, 100, 90, 5) == "candidate"
print("PASS: 6 scenarios + 6 boundary assertions")