Possible bug in DateList, DateObject etc returning negative years in 14.1

Question

DateList (and other date functions such as DateObject) were very good at catching ambiguous dates. However it looks like they have reverted and now seem to read DD-MMM-YYYY (Date, ShortMonth, Year seperated by "-") as negative years.

$Version

"14.1.0 for Microsoft Windows (64-bit) (July 16, 2024)"

DateList["15-Dec-2023"]

{-2023, 12, 15, 0, 0, 0.}

And in V14

$Version

"14.0.0 for Microsoft Windows (64-bit) (December 13, 2023)"

DateList["15-Dec-2023"]

{2023, 12, 15, 0, 0, 0.}

Edit:

Reported this to Wolfram and they replied

"It does appear that DateList is not properly parsing date strings in this format. An issue report has been forwarded to our developers."

Case 5169744

Answer 1

By the way, in Version 14.1 the whole pipeline for handling dates (and times) has been dramatically speeded up, most notably conversion from strings, as needed in the import of dates. Source

Furthermore, "YearSigned" was added as a possible element in DateString (but not to the autocomplete). Both of these likely contribute to the issue you are seeing.

(* Version 14.0 *)
DateString[{-2022, 2, 31}, "Year"]
(* "-2022" *)

(* Version 14.1 *)
DateString[{-2022, 2, 31}, "Year"]
(* "2022 BC" *)
DateString[{-2022, 2, 31}, "YearSigned"]
(* "-2022" *)

Is it a bug? Hard to decide, it certainly is slightly unexpected. What it could do is return an error message DateList::ambig, hinting that the interpretation is ambiguous.

In any case, I would say that you really shouldn't rely on the automatic interpretation of date strings, especially when you give it in an unconventional format. Just save yourself from issues and manually specify the elements:

DateList[{"15-Dec-2023", {"Day", "-", "MonthNameShort", "-", "Year"}}]
(* {2023, 12, 15, 0, 0, 0.} *)