diff --git a/src/wwvb/__init__.py b/src/wwvb/__init__.py
index 46467dd..e3e581b 100644
--- a/src/wwvb/__init__.py
+++ b/src/wwvb/__init__.py
@@ -411,7 +411,7 @@ class WWVBMinute(_WWVBMinute):
         year = cls.full_year(year)
         if ly is None:
             ly = isly(year)
-        return _WWVBMinute.__new__(cls, year, days, hour, minute, dst, ut1, ls, ly)
+        return super().__new__(cls, year, days, hour, minute, dst, ut1, ls, ly)
 
     @classmethod
     def full_year(cls, year: int) -> int:
@@ -686,7 +686,7 @@ class WWVBMinute(_WWVBMinute):
         return 0, False
 
     @classmethod
-    def fromstring(cls, s: str) -> WWVBMinute:
+    def fromstring(cls, s: str) -> Self:
         """Construct a WWVBMinute from a string representation created by print_timecodes"""
         s = _removeprefix(s, "WWVB timecode: ")
         d: dict[str, int] = {}
@@ -702,7 +702,7 @@ class WWVBMinute(_WWVBMinute):
         dst = d.pop("dst", None)
         ut1 = d.pop("ut1", None)
         ls = d.pop("ls", None)
-        d.pop("ly", None)
+        d.pop("ly", None)  # Always use calculated ly flag
         if d:
             raise ValueError(f"Invalid options: {d}")
         return cls(year, days, hour, minute, dst, ut1=ut1, ls=None if ls is None else bool(ls))
@@ -715,7 +715,7 @@ class WWVBMinute(_WWVBMinute):
         newut1: int | None = None,
         newls: bool | None = None,
         old_time: WWVBMinute | None = None,
-    ) -> WWVBMinute:
+    ) -> Self:
         """Construct a WWVBMinute from a datetime, possibly specifying ut1/ls data or propagating it from an old time"""
         u = d.utctimetuple()
         if newls is None and newut1 is None:
@@ -723,7 +723,7 @@ class WWVBMinute(_WWVBMinute):
         return cls(u.tm_year, u.tm_yday, u.tm_hour, u.tm_min, ut1=newut1, ls=newls)
 
     @classmethod
-    def from_timecode_am(cls, t: WWVBTimecode) -> WWVBMinute | None:  # noqa: PLR0912
+    def from_timecode_am(cls, t: WWVBTimecode) -> Self | None:  # noqa: PLR0912
         """Construct a WWVBMinute from a WWVBTimecode"""
         for i in (0, 9, 19, 29, 39, 49, 59):
             if t.am[i] != AmplitudeModulation.MARK:
diff --git a/src/wwvb/updateiers.py b/src/wwvb/updateiers.py
index 733e352..e8330fe 100755
--- a/src/wwvb/updateiers.py
+++ b/src/wwvb/updateiers.py
@@ -47,6 +47,7 @@ def update_iersdata(  # noqa: PLR0915
     """Update iersdata.py"""
     offsets: list[int] = []
     iersdata_text = _get_text(IERS_URL)
+    table_start = None
     for r in csv.DictReader(io.StringIO(iersdata_text), delimiter=";"):
         jd = float(r["MJD"])
         offs_str = r["UT1-UTC"]
@@ -79,6 +80,8 @@ def update_iersdata(  # noqa: PLR0915
 
         offsets.append(offs)
 
+    assert table_start is not None
+
     wwvb_text = _get_text(NIST_URL)
     wwvb_data = bs4.BeautifulSoup(wwvb_text, features="html.parser")
     wwvb_dut1_table = wwvb_data.findAll("table")[2]